file was produced from images produced by ,core ,historical ,literature in ,agriculture 7,,chla71 ,cornell ,university7 ,transcriber's ,note3 ,every effort has been made to replicate this text as faithfully as possible1 including obsolete and variant spellings and other inconsistencies4 ,text that has been changed to correct an obvious error is noted at the end of this ebook4 ,also1 on pages #dg-dh1 the ,greek letter theta is represented by ,,theta4 ,in chemical and mathematical notations1 a subscript is enclosed in braces and preceded by an underscore 7e4g41 ,h#b,o47 ,,agricultural ,,engineering ,,series ,e4 ,b4 ,,mccormick1 ,,consulting ,,editor ,,formerly ,,dean ,,of ,,engineering ,,division ,,kansas ,,state ,,agricultural ,,college ,,american ,,rural ,,highways ,mc,graw-,hill ,book ,co4 ,inc4 ,,publishers ,,of ,,books ,,for ,coal ,age -- ,electric ,railway ,journal ,electrical ,world -- ,engineering ,news-,record ,american ,machinist -- ,ingenieria ,internacional ,engineering ,mining ,journal -- ,power ,chemical ,metallurgical ,engineering ,electrical ,merchandising ,illustration3 ,frontispiece ,,american ,,rural ,,highways ,,by ,t4 ,r4 ,,agg1 ,c4,e4 ,,professor ,,of ,,highway ,,engineering ,,iowa ,,state ,,college ,,first ,,edition ,,mcgraw-,,hill ,,book ,,company1 ,,inc4 ,,new ,,york3 #bci ,,west #ci,,th ,,street ,,london3 #f #h ,,bouverie ,,st41 ,e4 ,c4 #d #aibj ,,copyright1 #aibj1 ,,by ,,the ,mc,g,r,a,w-,,hill ,,book ,,company1 ,,inc4 ,,preface ,,american ,,rural ,,highways was written for use as a text or reference in courses dealing with rural highways and intended for agricultural engineers1 students in agriculture and for short courses and extension courses4 ,the reader is assumed to have familiarity with drawing and surveying1 but the text is adapted primarily for students who do not receive training along the lines of the usual course in ,highway or ,civil ,engineering4 ,the text is intended to familiarize the student with the relation of highway improvement to national progress1 to indicate the various problems of highway administration and to set forth the usual methods of design and construction for rural highways in sufficient detail to establish a clear understanding of the distinguishing characteristics and relative serviceability of each of the common types of roadway surface4 ,experience with classes made up of students in agriculture or agricultural engineering and with trade school students in road making served as a guide in the selection and arrangement of the material4 ,detailed discussion of tests of materials and of the theory of design has to a considerable extent been eliminated as being outside of the scope of the course for which the text is intended4 ,in the preparation of ,american ,rural ,highways reference was had to many books on highway subjects and to current periodical literature4 ,wherever direct extracts were made from such source1 appropriate acknowledgment appears in the text4 ,t4 ,r4 ,,agg ,,ames1 ,,iowa1 ,,august #ah1 #aibj4 ,,contents ,,preface vii ,,chapter ,i ,,the ,,purpose ,,and ,,utility ,,of ,,highways ,transportation ,problem--,national in ,scope--,development in ,traffic--,location or ,farm to ,market ,traffic--,farm to ,farm ,traffic--,inter-,city ,traffic--,inter-,county and ,inter-,state ,traffic--,rural ,education--,rural ,social ,life--,good ,roads and ,commerce #a-ab ,,chapter ,,ii ,,highway ,,administration ,township ,administration--,county ,administration--,state ,administration--,federal ,administration--,special ,assessments--,zone ,method of ,assessing--,general ,taxation--,vehicle ,taxes--,sinking ,fund ,bonds--,annuity ,bonds--,serial ,bonds--,comparison of ,methods of ,issuing ,bonds--,desirability of ,road ,bonds #ac-bh ,,chapter ,,iii ,,drainage ,,of ,,roads ,the ,necessity for ,drainage--,importance of ,design--,surface ,drainage--,run-off--,ordinary ,design of ,ditches--,underground ,water--,tile ,drains--,lying ,tile--,culverts--,length of ,culvert-- ,farm ,entrance ,culverts--,metal ,pipe--,clay and ,cement ,concrete ,pipe--,concrete ,pipe--,endwalls for ,culverts--,reinforced ,concrete ,box ,culverts--,drop ,inlet ,culverts #bi-da ,,chapter ,,iv ,,road ,,design ,necessity for ,planning--,road ,plans--,problems of ,design-- ,preliminary ,investigations--,road ,surveys--,alignment-- ,intersections--,superelevation--,tracti ve ,resistance--,rolling ,resistance--,internal ,resistance--,air ,resistance--,effect of ,trades--,energy ,loss on ,account of ,grades--,undulating ,roads-- ,guard ,railing--,width of ,roadway--,cross ,section--,control of ,erosion--,private ,entrances--sthetics #db-fb ,,chapter ,v ,,earth ,,roads ,variations in ,soils--,variation in ,rainfall--,cross ,sections ,elevating ,grader--,maney ,grader--,slip ,scraper--,fresno ,scraper--,elevating ,grader ,work--,use of ,blade ,grader-- ,costs--,maintenance--,value of ,earth ,roads #fc-gc ,,chapter ,,vi ,,sand-,,clay ,,and ,,gravel ,,roads ,the ,binder--,top-soil or ,natural ,mixtures--,sand-clay on ,sandy ,roads--,sand-clay on ,clay or ,loam--,characteristics--,natural ,gravel--,the ,ideal ,road ,gravel--,permissible ,size of ,pebbles-- ,wearing ,properties--,utilizing ,natural ,gravels--,thickness of ,layer--,preparation of the ,road--,trench ,method--,surface ,method--,maintenance #gd-hh ,,chapter ,,vii ,,broken ,,stone ,,road ,,surfaces ,design--,properties of the ,stone--,kinds of ,rocks used for ,macadam--,sizes of ,stone--,earth ,work--,foundation for the ,macadam--,telford ,foundation--,placing the ,broken ,stone-- ,rolling--,spreading ,screenings--,bituminous ,surfaces--,maintenance ,characteristics #hi-ig ,,chapter ,,viii ,,cement ,,concrete ,,roads ,destructive ,agencies--,design--,concrete ,materials--,fine ,aggregate--,proportions--,measuring ,materials--,preparation of the ,earth ,foundation--,placing ,concrete for ,two-course ,road--,curing the ,concrete--,expansion ,joints--,reinforcing--,bituminous ,coatings on ,concrete ,surfaces--,characteristics--,maintenanc e #ih-aje ,,chapter ,,ix ,,vitrified ,,brick ,,roads ,vitrified ,brick--,paving ,brick--,repressed ,brick--,vitrified ,fiber ,brick--,wire-cut-lug ,brick--,tests for ,quality--,other ,tests-- ,foundation--,sand ,bedding ,course--,sand ,mortar ,bedding ,course-- ,green ,concrete ,bedding ,course--,bituminous ,fillers--,mastic ,fillers--,marginal ,curb #ajf-aae ,,chapter ,x ,,bituminous ,,road ,,materials ,,and ,,their ,,use ,classes of ,bituminous ,materials--,coal ,tar--,water ,gas ,tar--,natural ,asphalt--,petroleum ,asphalt--,mixtures--,classification ,according to ,consistency--,road ,oils--,liquid ,asphalts--,asphalt ,cements-- ,fillers--,bitumen--,specifications--,su rface ,treatments--,applying the ,bituminous ,binder--,finishing the ,surface--,patching-- ,penetration ,macadam--,foundation--,upper or ,wearing ,course-- ,patching ,characteristics--,hot ,mixed ,macadam--,foundation--,sizes of ,stone--,mixing the ,wearing ,stone--,placing and ,wearing ,surface--,seal ,coat--,characteristics--,asphaltic ,concrete-- ,bitulithic or ,warrenite--,topeka ,asphaltic ,concrete--,foundation --,placing the ,surface--,characteristics #aaf-abi ,,chapter ,,xi ,,maintenance ,,of ,,highways ,petrol ,maintenance--,gang ,maintenance--,maintenance of ,earth1 ,sand-clay1 ,gravel and ,macadam ,roads #acj-acd ,index #ace ,,american ,,rural ,,highways ,,chapter ,i ,,the ,,purpose ,,and ,,utility ,,of ,,highways ,,the ,,development ,,of ,,highway ,,systems ,transportation ,problem4--,public highways1 like many other familiar things1 are utilized constantly with little thought of how indispensable they are to the conduct of the business of a nation or of the intimate relation they bear to the everyday life of any community4 ,the degree to which a nation or a community perfects its transportation facilities is an index of its industrial progress and public highways constitute an important element in the national transportation system4 ,it is to be expected that the average citizen will think of the public highway only when it affects his own activities and that he will concern himself but little with the broad problem of highway improvement unless it be brought forcibly to his attention through taxation or by publicity connected with the advancement of specific projects4 ,national in ,scope4--,the improvement and extension of the highway system is of national importance just as is development and extension of railways1 and concerted action throughout a nation is a prerequisite to an adequate policy in regard to either4 ,it is inconceivable that any community in a nation can prosper greatly without some benefit accruing to many other parts of the country4 ,increased consumption1 which always accompanies material prosperity1 means increased production somewhere1 and people purchase from many varied sources to supply the things that they want4 ,good transportation facilities contribute greatly to community prosperity and indirectly to national prosperity1 and the benefits of highly improved public highways are therefore national in scope4 ,this fact has been recognized in ,europe1 notably in ,england1 ,france and ,belgium1 where the public highways are administered largely as national utilities4 ,until recent years1 highway improvement in the ,united ,states has been subordinated to other more pressing public improvements1 but during the ,world ,war the inadequacy of the transportation system of the ,united ,states became apparent4 ,while such an unprecedented load upon transportation facilities may not recur for many years1 it has become apparent that more rapid progress in highway improvement is necessary and in the ,united ,states the subject is now likely to receive attention commensurate with its importance4 ,development of ,traffic4--,the character and extent of the highway improvement needed in any locality is dependent entirely on the demands of traffic4 ,in sparsely settled areas1 particularly those that are semi-arid or arid1 the amount of traffic on local roads is likely to be small and the unimproved trails or natural roads adequate4 ,but as an area develops either on account of agricultural progress or the establishment of industrial enterprises1 the use of the public highways both for business and for pleasure increases and the old trails are gradually improved to meet1 at least to some degree1 the new demands of traffic4 ,in sparsely settled areas1 it is possible for the public to accommodate its use of the highways to the physical condition thereof1 and business is more or less regulated according to the condition of the roads4 ,this is not always pleasant or economical but is the only possible arrangement4 ,in populous districts1 with diversified activities1 it becomes imperative to have year-round usable roads in order to transact with reasonable dispatch the regular business of the industries4 ,anything less will handicap normal community progress4 ,the advent of the motor driven vehicle in the ,united ,states has resulted in a greatly increased use of the public highways of agricultural areas1 even of those that are sparsely populated1 because of the convenience of the motor vehicle both for passenger and for freight service4 ,probably in excess of #ij per cent of the tonnage passing over the rural highways in the ,united ,states is carried by motor vehicles4 ,this class of traffic has really just developed and no one can predict what it will be in ten years1 yet it has already introduced into the highway problem an element that has revolutionized methods of construction and maintenance4 ,a different set of traffic conditions exists in those parts of the ,united ,states where large areas are devoted primarily to industrial pursuits1 the agricultural development being of secondary importance4 ,public highways connecting the industrial centers are indispensable adjuncts to the business facilities in such communities and are ordinarily subjected to a very large volume and tonnage of traffic consisting principally of motor vehicles4 ,the roads first selected for improvement will not be those serving the agricultural interests of the district1 but rather those serving the industrial centers4 ,inter-city roads of great durability and relatively high cost are necessary for such traffic conditions4 ,not infrequently the transportation needs will require a system of both inter-city and rural highways in the same community4 ,there are few areas in the ,united ,states where there is no agricultural development4 ,it is apparent therefore that the nature of the highway systems and the administrative organization under which they are built and maintained will differ in various states or areas according to the nature of development of that area agriculturally and industrially4 ,in planning improvements of highway systems1 it is recognized that one or more of several groups of traffic may be encountered and that the extent and nature of the improvement must be such as will meet the requirements of all classes of traffic1 the most important being first provided for1 and that of lesser importance as rapidly as finances permit4 ,,kinds ,,of ,,traffic ,,on ,,public ,,highways ,local or ,farm to ,market ,traffic4--,in strictly agricultural communities the principal use of the highways will pertain to agricultural activities and most of it will be between the farm and the most convenient market center4 ,in the ordinary state1 the number of rural families will not average more than six to eight per square mile1 but in some districts it may reach twenty families per square mile4 ,the travel from the district around a market center will originate in this rather sparsely populated area and converge onto a few main roads leading to market4 ,the outlying or feeder roads will be used by only a few families1 but the density of traffic will increase nearer the market centers and consequently the roads nearer town will be much more heavily traveled than the outlying ones4 ,it is apparent therefore that considerable difference may exist in the kind of construction adequate for the various sections of road where farm traffic is the principal consideration4 ,this traffic is made up of horse drawn wagons1 transporting farm products and of horse drawn and motor passenger vehicles1 the motor traffic comprising #hj per cent or more of the volume of traffic and a greater per cent of the tonnage4 ,motor trucks are now employed to some extent for marketing farm products and1 where surfaced highways have been provided1 this class of traffic is superseding horse drawn traffic4 ,farm to ,farm ,traffic4--,in the ordinary prosecution of farming operations1 a considerable amount of neighborhood travel is inevitable4 ,farmers help each other with certain kinds of work1 exchange commodities such as seed1 machinery and farm animals and visit back and forth both for business and pleasure4 ,to accommodate this traffic1 it is desirable to provide good neighborhood roads4 ,traffic of this sort follows no particular route and can to some extent accommodate itself to the condition of the highways without entailing financial loss1 although some discomfort and some inconvenience may result from inadequate highway facilities4 ,this traffic will be partly motor and partly horse drawn1 but the proportion of motor driven is large4 ,inter-city ,traffic4--,in strictly agricultural districts there is a large amount of travel between towns1 both for business and for pleasure4 ,the pleasure travel is mostly in motor vehicles and a considerable part of the business traffic is the same1 although horse drawn vehicles are employed to some extent4 ,in industrial districts there is a large volume of this class of traffic consisting of motor passenger vehicles used for business and for pleasure and of motor freight vehicles used for general business purposes4 ,in addition1 there is certain to be a large amount of motor truck freight traffic incident to the particular industrial pursuits of the cities4 ,where adequate public highways connect industrial centers1 there is invariably a very large amount of inter-city traffic1 due in part to the needs of industry and in part to concentration of population in industrial centers4 ,inter-,county and ,inter-,state ,traffic4--,automobile touring is a popular means of relaxation1 especially on the part of those who live in the cities1 although it is by no means confined to them4 ,traffic of this kind follows the routes where roads are best and passes entirely across a county1 attracted by some public gathering4 ,often it is inter-state in character1 made up of tourists who are traveling to distant pleasure resorts4 ,such traffic at present constitutes a relatively small part of the travel on public highways1 except on certain favorable routes1 but as the wealth of the country increases and good touring roads are numerous1 long distance travel will increase and will eventually necessitate the construction of a number of well maintained national highways1 located with reference to the convenience of the automobile tourist4 ,,public ,,highways ,,and ,,community ,,life ,it is well to recognize the intimate relation public highways bear to the economic progress of a nation4 ,normal development of all of the diverse activities of a people depends very largely upon the highway policy that is adopted and whether the actual construction of serviceable roads keeps pace with transportation needs4 ,rural ,education4--,it has become increasingly apparent during the ,world ,war that the demand upon ,north ,america for food stuffs is to become more and more insistent as the years pass4 ,already the consumption in the ,united ,states has approached quite closely to the average production and yet the population is constantly increasing4 ,the time is not far distant when greater production will be required of the agricultural area in ,north ,america in order to meet the home demand for foodstuffs1 and many thousands of tons will be needed for export4 ,this need can only be met by agricultural methods that will increase greatly the present yield of the soil4 ,the adoption of better agricultural methods must of necessity be preceded by the technical training of the school children who will be the farmers of the next generation1 which can best be accomplished in graded schools with well equipped laboratories and with suitably trained teachers4 ,the problem of providing such schools in rural communities has1 in some instances1 been solved by consolidating a number of rural school districts and constructing a well equipped building to accommodate the students from an area several miles square4 ,an educational system of this sort can reach its highest usefulness only when adequate public highways facilitate attendance of pupils4 ,the whole trend of rural educational progress is toward a system which is predicated upon a comprehensive highway policy in the district4 ,rural ,social ,life4--,closely allied to the rural educational problem is the rural social problem4 ,motor cars and good roads do a great deal to eliminate the isolation and lack of social opportunity that has characterized rural life in the ,united ,states4 ,a high order of citizenship in rural communities is essential to the solution of many problems of rural economics1 and such citizens will not live away from the social opportunities of modern life4 ,the rural school house and the rural church may become social centers and local plays1 moving picture shows and lectures and entertainments of other kinds made available to those who live in the country4 ,their enjoyment of these social opportunities will be much more general if the public highways are at all times in a condition to be traveled in comfort4 ,good homes and good schools on good roads are prerequisites to the solution of many rural problems4 ,if there is opportunity for those who live in the cities to get some adequate idea of rural life and the conditions under which farming operations are carried on it will correct many misunderstandings of the broad problems of food production and distribution4 ,reference has frequently been made to the seeming desire on the part of city people to get into the country1 and1 by facilitating the realization of this desire1 a great social service is rendered4 ,good ,roads and ,commerce4--,that good highways are almost as necessary as are railroads to the commercial development of a nation is recognized but1 unlike the railroads1 the highways are not operated for direct profit and the responsibility of securing consideration of the demand for improvements is not centralized4 ,therefore1 sentiment for road improvement has been of slow growth1 and important projects are often delayed until long after the need for them was manifest4 ,movements to secure financial support for highway improvement must go through the slow process of legislative enactment1 encountering all of the uncertainties of political action1 and the resulting financial plan is likely to be inadequate and often inequitable4 ,the whole commercial structure of a nation rests upon transportation1 and the highways are a part of the transportation system4 ,the highway problem can never receive adequate consideration until public highways are recognized as an indispensable element in the business equipment of a nation4 ,during the ,world ,war all transportation facilities were taxed to the limit1 and motor trucks were utilized for long distance freight haulage to an extent not previously considered practicable4 ,as a result1 the interest in the motor truck as an addition to the transportation equipment of the nation1 has been greatly stimulated4 ,many haulage companies have entered the freight transportation field1 delivering commodities by truck to distances of a hundred miles or more4 ,the part the motor truck will play in the future can only be estimated1 but it seems clear that the most promising field is for shipments destined to or originating in a city of some size and a warehouse or store not on a railroad spur1 and especially when the shipments are less than car load lots4 ,the delays and expense incident to handling small shipments of freight through the terminals of a large city and carting from the unloading station to the warehouse or other destination constitute a considerable item in the cost of transportation4 ,mr4 ,charles ,whiting ,baker1 ,consulting ,editor of ,engineering ,news-,record1 states3#a #a ,engineering ,news ,record1 ,july #aj1 #aiai4 ,it costs today as much to haul a ton of farm produce ten miles to a railway station as it does to haul it a thousand miles over a heavy-traffic trunk-line railway4 ,it often costs more today to transport a ton of merchandise from its arrival in a long train in the freight yard on the outskirts of a great city to its deposit in the warehouse of a merchant four or five miles away than it has cost to haul it over a thousand miles of railway line4 ,nevertheless it seems probable that new methods of operating the motor truck transport1 and possibly new types of trucks or trucks and trailers will be developed so that freight traffic over many roads will be of considerable tonnage and an established part of the transportation system of the nation4 ,in the article above referred to are given the following data relative to the cost of hauling on improved roads by motor truck and these cost estimates are based on the best information available at this time4 ,they should be considered as approximate only1 but serve to indicate the limitations of the truck as a competitor of the steam railway4 ,,table #a ,,truck ,,operation ,,costs1 ,,from ,,reports ,,by ,,six ,,motor ,,truck ,,operators1 ,,direct ,,charges ,,per ,,day ---------------------------------------- ---------------------- ,a ,b ,c ,d ,e ,f ,average ,total ---------------------------------------- ---------------------- ,driver #e4jj #e4bj #e4jj #e4jj #e4ag #e4ej #e4ac ,tires #c4jj #c4ge #b4jj #b4jj #b4jj #c4jj #b4fh ,oil1 etc4 4#cj 444 4#cj 4#ej 4#be 4#be 4#ce ,gasoline #c4jj #d4jj #c4ej #d4fe #b4jh #c4ge #c4ej ------ #aa4ff ---------------------------------------- ---------------------- ,,indirect ,,charges ,,per ,,day ---------------------------------------- --------------------- ,average ,a ,b ,c ,d ,e ,f ,total ---------------------------------------- --------------------- ,depreciation #c4ej #d4ai #c4fj #c4dj #c4fg #d4jj #c4gg ,interest #a4bj #a4bf #a4jh #a4bb #a4aj #a4jj #a4ae ,insurance #a4ej #b4ed #a4bf #b4aj 4#hf 4#ej #a4dg ,garage #a4jj #a4bj #a4jj #a4jj 4#hi #a4jj #a4ja ,maintenance 4#ej 444 4#ej 444 #a4jj 444 4#ge ,overhaul #a4cc #b4ge #a4hj #a4fj #b4jj #c4jj #b4jg ,license 4#ag 4#bg 4#bj 4#bj 4#bj 4#bj 4#bj ,body upkeep 4#be 444 4#cj 4#aj 4#dj 444 4#bg ---- #aj4fi ,supervision 4#ej #b4ic #b4je #a4ij 444 444 #a4ij #a4ij ,lost time #b4bj 444 #a4fg #c4dj #b4ej #a4ig #b4eg #b4eg ----- ----- ----- ----- ----- ----- ----------- #bc4de #bh4ji #bd4bf #bh4jg #bb4ab #bd4ag #bf4hb ---------------------------------------- --------------------- ,,table #b ,,overhead ,,charges ,,per ,,year ,,for ,a #e-,,ton ,,capacity ,,gasoline ,,motor ,,truck ,,running ,,an ,,average ,,of #ej ,,miles ,,per ,,day ,,for #bdj ,,days ,,per ,,year ,driver's wages#a #aejj ,depreciation 7#bj on #fjjj investment7 #abjj ,interest 7#f on #fjjj investment7 #cfj ,insurance #dej ,garage 7rental1 upkeep1 etc47 #cjj ,maintenance1 minor repairs and supplies1 tire chains1 tools1 lamps1 springs1 equipment1 etc4 7estimated7 #cjj ,complete overhaul once a year #fjj ,license fee #fj ,body upkeep1 repairs1 painting1 etc4 #ij ,supervision #fif ----- ,total per annum #eeef ,overhead charges per day for #bdj days in the year1 actual operation #bc4ae ,overhead charges per mile for #ej miles per day 4#dfc #a ,in the above table the driver's wages have been placed under overhead charges because the driver is paid by the month and his wages continue even though the truck is idle because of repairs1 bad weather or lack of business1 unless1 of course1 the idleness should be of long duration1 when the driver might be laid off4 ,,direct ,,charges ,,per ,,day ,,and ,,per ,,mile ,,for #e-,,ton ,,truck ,,operated ,,as ,,above ---------------------------------------- -------------------------- ,cost ,cost per day per mile ---------------------------------------- -------------------------- ,tires 7based on present tire guarantee7 #c4jj #j4jf ,lubricants 4#ej 4#ja ,gasoline 7#c-a_/b miles per gal41 #ad gal4 at #be;c7 #c4ej 4#jg ----- ----- #g4jj #j4ad ---------------------------------------- -------------------------- ,total of overhead and direct charges for #bdj days per year operation1 per day #cj4ae ,per mile 4#fjc ,cost per ton-mile for full loads one way and empty returning 4#bdab ,cost per ton-mile for full loads one way and half load returning 4#af ,the significance of these figures becomes apparent when they are compared with the cost of hauling freight over trunk-line railways with heavy traffic where the cost per ton-mile1 including terminal charges1 ranges from #a4g mills per ton-mile to #d4d mills per ton-mile4 ,in view of these facts it seems reasonable to suppose that motor vehicles for use on the public highways are more likely to be employed to supplement the rail transport than to compete with it4 ,to the actual cost of operation of motor trucks given in ,table #b1 there should be added the proportionate cost of maintaining the highway for the use of the truck1 which is partly covered by the item ,license ,fee in the table4 ,the license fee would necessarily be considerably larger if it were to compensate adequately for the wear on the highways over which the trucks operate4 ,this will still further increase the cost of hauling by motor truck4 ,motor trucks are employed for many kinds of hauling where their speed and consequently their daily capacity is an advantage over team hauling that is decidedly worth while4 ,it probably could be shown that for many kinds of hauling1 teams are more economical than motor trucks1 but when promptness and speed and the consequent effect on dependent activities are considered1 the motor truck often has a distinct advantage1 and the use of the truck to replace horse drawn vans is progressing rapidly4 ,this is true not only in the cities1 but also in the smaller towns and in the country4 ,motor trucks have been adopted in a great many communities for delivery of farm products to market1 and this use of the truck is certain to increase rapidly4 ,but trucks in this service will use the secondary roads as well as the main or primary roads4 ,these observations emphasize the extent to which the highway policy of the nation must be predicated on the use of the highways by motor vehicles4 ,,chapter ,,ii ,,highway ,,administration ,the systems of highway administration extant in the various political units in the ,united ,states present a patchwork of overlapping authority and undetermined responsibility4 ,highway laws are being constantly revised by state legislatures and with each revision there is some change in administrative methods and often the changes are revolutionary in character4 ,in most states1 the trend is away from county and township administration and toward state administration1 with provision for considerable participation by the federal government4 ,it will be pertinent to consider briefly the present functions of each of the administrative authorities having duties in connection with highway work in the ,united ,states1 although these duties vary greatly in the several states and change periodically with the action of legislatures4 ,township ,administration4--,township or ,town authority is a survival of the old ,new ,england town government and the town board consists of three or more trustees who hold office for fixed terms4 ,the usual term is three years1 but is less in some states4 ,the incumbent is generally a man who has other responsibilities of a public or private nature and who gives but little of his time to highway matters4 ,in some states the pay is a fixed annual salary and in others a per diem with some limitation on the amount that may be drawn in any one year1 which limitation may be statutory or may be by common consent4 ,the township highway commissioners or trustees have jurisdiction over certain of the roads in the township1 usually best described as all roads not by law placed under the jurisdiction of some other authority4 ,in certain instances1 the township authorities have charge of all of the roads in the township1 which would mean that no county or state roads happened to be laid out in that township4 ,it is a matter of general observation that the trend of legislation is toward removing from the jurisdiction of the township officials all roads except those upon which the traffic is principally local in character4 ,the actual mileage of roads in the ,united ,states that is at present administered by township officials is large1 probably constituting not less than seventy per cent of the total mileage4 ,in most states the township officials are responsible for the maintenance of the roads under their jurisdiction and also supervise such new construction as is undertaken4 ,this includes the construction of culverts and bridges as a rule1 but in some states the county board of supervisors is responsible for all of the bridge and culvert work on the township roads4 ,in other states1 the township board is responsible only for bridges or culverts that cost less than a certain amount specified by law 7usually about #ajjj7 and the county board provides for the construction and upkeep of the more expensive bridges and culverts4 ,funds for the work carried out by the township road officials are obtained by general taxation1 the amount that may be levied being limited by statute and the actual levy being any amount up to the maximum that the township board deems necessary for its purposes4 ,it is the general observation that the tax levy is usually the maximum permitted by law4 ,in many states1 township officials are permitted to issue bonds for road construction1 almost invariably1 however1 with the restriction that each issue must be approved by the voters of the township4 ,there is always a provision that the total amount of bonds outstanding must not exceed the constitutional limit in force in the state4 ,in several states1 the townships have large amounts of road bonds outstanding4 ,county ,administration4--,in some states the county is the smallest administrative unit in the road system4 ,a county board1 called the board of county supervisors or board of county commissioners consisting of from three to fifteen members1 is the administrative authority4 ,its members are elected for fixed terms which vary in length from one to five years4 ,the county board usually has many public responsibilities other than highway administration1 and is generally made up of men with considerably more business ability than the average township board4 ,the county board has jurisdiction over all of the highways in the county in some states1 and in others it has charge of only the more important highways4 ,in most states1 the laws set forth specifically what highways shall be under the jurisdiction of the county authorities4 ,in addition to having direct supervision of the improvement and maintenance of the roads assigned to county administration1 the county boards in some states arrange for the construction of all culverts and bridges on the roads that are under township supervision1 or at least the more expensive bridges and culverts on such roads4 ,sometimes this is accomplished by granting county aid for township bridges1 under which system the county pays a part of the cost of the construction of bridges on the township roads4 ,the amount of aid varies1 but is generally about one-half of the cost1 and the township and county officials jointly assume the responsibility of arranging for the construction by contract or otherwise4 ,the county board obtains funds for road work through a direct tax on all property in the county1 the maximum rate being limited by statute4 ,county boards are also authorized to issue bonds for road construction under statutory restrictions and limitations similar to those effective in the township as to total amount issued1 and many millions of dollars' worth of highway bonds have been issued by county authorities in the ,united ,states4 ,state ,administration4--,in a state1 the administrative authority in highway matters is vested in a board of commissioners usually consisting of three or more members4 ,in a few states1 the administrative authority is delegated to a single commissioner4 ,where the authority is vested in a board1 that board is usually appointed by the governor4 ,in several states one or more members of the commission hold that position ex officio2 for example1 in several states the governor is by law a member of the commission1 in others the secretary of state or the dean of engineering at the ,state ,university or the state geologist is a member of the commission4 ,where the administrative authority is a single commissioner he may be elected along with other state officers1 but this is the case in only a few states4 ,the authority of the state highway department varies in the several states1 but in general the departments serve in the dual capacity of general advisers to the county and township authorities on road matters and as the executive authority responsible for the construction of those highways that are built entirely or in part from state or federal funds4 ,state highway departments consist of the commission or commissioner1 and the technical and clerical staff required to perform the duties imposed on the state organization4 ,to some extent the state highway departments are able to encourage economical and correct construction of highways by the township and county authorities by furnishing them standard plans and specifications and by formulating regulations to govern the character of construction1 but such efforts are likely to be more or less ineffective unless the state authority has supervision of the allotment of state or federal funds to the various counties and townships4 ,nevertheless1 most state highway departments do a great deal of advisory work in connection with the highway construction carried out by county and township authorities4 ,state highway departments are supported by funds obtained in various ways1 laws differing greatly in this respect4 ,the necessary support is in some states appropriated from funds obtained by general taxation1 and is in others obtained from automobile license fees4 ,in still others1 the funds are secured by a combination of the two methods mentioned above4 ,in addition to these support funds1 a certain part of the money obtained as federal aid may be employed for the engineering and inspection costs on federal aid roads4 ,the above mentioned funds are required to maintain the state highway department4 ,in addition1 the departments have supervision of the expenditures of construction funds which can be used for road construction and maintenance1 and may not be expended for salaries or other overhead expense4 ,in a number of states1 automobile license fees are set aside for financing road construction and maintenance1 and the work paid for from the fees is carried out under the supervision of the state highway department4 ,in a number of instances1 state bonds have been issued for road construction1 and the expenditure of the proceeds of the sale of road bonds has usually been supervised by the state highway department4 ,all federal aid funds allotted to a state must be expended under the direction of the state highway department4 ,federal ,administration4--,federal authority in highway work is vested in the ,bureau of ,public ,roads of the ,united ,states ,department of ,agriculture4 ,the official head is the ,secretary of ,agriculture1 but the administrative head is the ,director of the ,bureau4 ,in this ,bureau are the various instrumentalities needed for carrying on investigations and furnishing information to the various states on highway subjects4 ,the ,bureau also supervises the construction of federal aid roads in a general way through district engineers1 each of whom looks after the work in several states4 ,funds for the support of the ,bureau of ,public ,roads are obtained from congressional appropriations to the ,department of ,agriculture and from a percentage of the funds appropriated for federal aid4 ,federal aid is money appropriated by ,congress to be distributed to the various states to stimulate road construction4 ,it is granted to the states on the condition that the states will expend at least an equal amount on the projects involved4 ,the states in turn usually give a suitable part of the state allotment to each county4 ,there are various limitations as to the amount of federal aid per mile of road and the type of construction that may be employed1 but these are matters of regulation that change from time to time4 ,it will be seen that each of the administrative authorities1 except the ,bureau of ,public ,roads1 is to some extent subservient to a higher authority1 and the ,bureau of ,public ,roads is supervised by the ,united ,states ,congress4 ,considerable diplomacy is required on the part of any administrative authority if his contact with other officials is to be without friction4 ,this is especially true in connection with the formulation of a policy regarding the types of construction to be adopted for an improvement4 ,the responsibility for the selection is variously placed on the township1 county or state authority1 the laws not being uniform in this respect4 ,if state or federal funds are allotted to an improvement1 the state authority either makes the selection of the type of construction or the selection is made by some subordinate authority subject to the approval of the state highway department4 ,where the improvement is paid for exclusively with township or county funds1 the selection is often made by the township or county authority without review by higher authority4 ,many abuses have crept into highway administration through the unscrupulous methods of promoters of the sale of road materials or road machinery4 ,a great deal of the selling activity of the agents for these commodities is entirely irreproachable1 but it is well known that such is not always the case4 ,as a result1 the tendency of legislation is to require the state highway department to approve contracts for materials or construction entered into by the township or county authorities4 ,the state highway departments can secure the requisite technical experts to determine the merits of materials and equipment and1 in spite of some glaring examples of inefficiency or worse1 have made a good record for impartiality and integrity as custodians of the funds for which they are responsible4 ,,highway ,,finance ,the paramount problem in highway administration is the development of an adequate financial plan for carrying on road improvement4 ,the necessary expenditures are enormous1 although the money so expended is probably much less than the actual benefit resulting from the improvements4 ,special ,assessments4--,there is presumed to be a direct and recognized benefit conferred on farm lands by the construction of improved highways adjacent thereto4 ,therefore1 it is equitable to charge a part of the cost against the lands so benefited4 ,the principle of paying for public improvements by a special assessment upon private property has been long established and a large proportion of the public improvements in the cities and towns have been made financially possible through the medium of special assessments on abutting and adjacent property4 ,the same principle has been applied to the financing of drainage projects for reclaiming farm lands4 ,recently the special assessment method has come into limited use in financing rural highway improvements4 ,the policy in such cases is to assess the abutting and adjacent property in a zone along the improved road for a percentage of the cost of the improvement4 ,the amount so assessed does not ordinarily exceed one-fourth of the total cost of the improvement and may be considerably less4 ,the assessment is spread over an area extending back from one to six miles from the improved road4 ,the assessment area is generally divided into about four zones parallel to the road4 ,the zone next the road is assessed at a rate arbitrarily determined as a fair measure of the benefit1 and each succeeding zone is assessed at a somewhat lower rate4 ,generally about three-fourths of the total assessment is placed on the half of the assessment area lying next to the road4 ,many systems of making assessments have been proposed which are mechanical in application after the area and rate of distribution of benefit have been established1 but in practice it is always found necessary to make adjustments on individual parcels of land because of variation in benefits received and it is impossible to eliminate the exercise of human judgment in equalizing the assessments4 ,zone ,method of ,assessing4--,the area to be assessed on each side of the improved road is divided into zones usually four in number1 but a larger or smaller number of zones may be adopted4 ,the rate for each zone is then arbitrarily determined4 ,for a typical case1 the first of four zones would receive an assessment of #ej per cent of the amount to be borne by the area2 the second zone #be per cent1 the third #ae per cent and the fourth #aj per cent4 ,other percentages sometimes adopted are #de1 #be1 #bj and #aj and #fj1 #bj1 #ae and #e4 ,the set of percentages first mentioned seems to insure the most equitable distribution for an area all of which is substantially equally productive4 ,when a road1 for the improvement of which an assessment is being made1 lies on two or more sides of a parcel of land all of which is within the assessment area1 the rate is arbitrarily reduced to relieve that parcel of land somewhat1 or the assessment is first spread as above outlined and afterward equalized as judgment dictates4 ,in applying the zone method some difficulty is encountered in determining an equitable distribution on those parcels of land lying partly in one zone and partly in another1 but the rate may be arrived at with reasonable accuracy by pro-rating in accordance with the exact conditions4 ,in4 ,fig4 #a1 let it be assumed that the assessment area is to be two miles wide1 one mile on each side of the road and the various ownerships to be indicated by the parcels of land numbered #a to #h1 as shown4 ,each zone for the assessment of the #c-a_/d mile section is #a_/d mile wide and the rates for the several zones are #ej1 #be1 #ae and #aj per cent respectively4 ,let it be assumed that the portion of the cost of the #c-a_/d miles of road to be assessed on the area shown is #bj1jjj4 ,the assessment would then be as follows3 ---------------------------------------- -------------------- ,rate frontage on ,amount of ,parcel ,rate improved road ,assessment ,assessment assessment units per unit#a #a #b #c #d #e ---------------------------------------- -------------------- #a a #ej #ej #bfdj #acb1jjj #j4jaffee #aeeh4df b #ge #ge #acbj #ii1jjj #aaec4ij #b #dj #dj #bfdj #aje1fjj #abcj4gg #c #aj #aj #bfdj #bf1djj #cjg4fi #d #be #be #acbj #cc1jjj #chd4ff #e #bhe #he #ebhj #ddh1hjj #ebcj4hh #f #ae #ae #ebhj #gi1bjj #ibc4jh #g #bfe #fe #gibj #ead1hjj #fjjj4jj #h #ce #ce #gibj #bgg1bjj #cbcj4gg ------------------- ----------- #a1gaf1jjj #bjjjj4jj ---------------------------------------- -------------------- #a ,the assessment per unit is obtained by dividing the total assessment by the total of column three4 #b ,on these two parcels1 it is decided that more than half of the zone rate should apply to the half of the zone toward the improved road1 but some modification of the rates adopted might be justified4 ,illustration3 ,fig4 #a ,the assessment of the cost of the east and west one-mile section of road is made up in like manner1 and let it be assumed that the portion of the cost of this road that is to be assessed on the area shown is #eejj4 ,the assessment area will be one mile wide and each zone one-fourth mile in width and the rates for each zone the same as before4 ---------------------------------------- -------------------- ,rate frontage on ,amount of ,parcel ,rate improved road ,assessment ,assessment assessment units per unit ---------------------------------------- -------------------- #a a #ge #ge x #acbj #ii1jjj #j4jajdag #ajca4be b #ae #ae x #bfdj #ci1fjj #dab4di #b #ge #ge x #bfdj #aih1jjj #bjfb4ec #c #ej #ej x #acbj #ff1jjj #fhg4ea #d a #be #be x #acbj #cc1jjj #gef4be b #ae #ae x #bfdj #ci1fjj #e #aj #aj x #ccjj #cc1jjj #cdc4gc #f #aj #aj x #aihj #ai1hjj #bjf4bd ------------- ------------- #ebh1jjj #eejj4jj ---------------------------------------- -------------------- ,it will be noted that the combined assessment for the two sections of road is especially heavy on parcels #a1 #b and #c4 ,in order to prevent unjust charges against such properties1 laws usually limit the total assessment against any parcel of land to a fixed percentage of a fair market value or of the assessed value4 ,the assessment on these parcels would be reduced as seemed expedient and the deficit would be distributed over the remainder of the area in the same manner as the original assessment was spread4 ,in practice such re-distribution is ordinarily made by the arbitrary adjustment in accordance with what the authorized officials consider to be fair and equitable4 ,the method outlined is merely a mechanical means of securing distribution and must not be considered as an infallible method of making the assessment4 ,it is always necessary to review the results in the light of the actual benefits to be presumed for each parcel of land4 ,nevertheless1 the method outlined will prove equitable in a majority of cases4 ,general ,taxation4--,there is a general community benefit derived from the construction of good roads in that the actual cost of marketing farm products is lessened with a resulting lowering of the price to the consumer4 ,the benefit also accrues from the greater facility with which all community business may be conducted4 ,the introduction of better opportunities for social1 religious and educational activities in the rural districts which results from improved highways is also a community benefit of no mean importance4 ,a part of the cost of road improvement may therefore be equitably paid from funds obtained by general taxation4 ,a considerable portion of the current expense of maintaining the township and county highway work and at least a part of the cost of maintaining state highway activities is met from funds obtained by general taxation4 ,likewise1 the funds required for the amortization of bond issues are often obtained from general taxation although vehicle license fees are sometimes used for that purpose4 ,general taxes are levied on all taxable property in a political unit under statutory provisions regulating the amount of the levy and the purpose for which the revenue is to be used4 ,in the aggregate1 the road taxes are large but in the township or county the rate is generally small compared to some other taxes1 such as the school tax4 ,vehicle ,taxes4--,the great direct benefit derived by those who actually operate vehicles over the roads justifies the policy of requiring a vehicle to pay a license fee in lieu of other taxes1 the funds so obtained to be used for the construction and maintenance of public highways4 ,in practice1 this method has already been applied to motor vehicles in most states and has proven to be an important source of revenue4 ,its application to horse-drawn vehicles has not been attempted1 due probably to the fact that such horse-drawn vehicles as use the public highways are also employed about the farm or in the towns and the determination of an equitable basis for taxation involves many difficulties4 ,the rate of the fee for motor vehicles should be based on their destructive effect on the road so far as that is possible4 ,the scale of fees should therefore take account of weight and speed of vehicle and if the license is in lieu of all other taxes1 it should also be graduated with the cost of the vehicle4 ,when funds are thus derived1 every precaution should be taken to insure that the money is used judiciously for construction and especially for maintenance on those roads most useful to motor traffic4 ,highway ,bonds4--,bond issues for road improvement afford a means of constructing roads and paying for them while they are being used4 ,a very large volume of such bonds are outstanding in the ,united ,states4 ,road bonds should be issued only for durable types of improvement and the life of the bond should be well within the probable useful life of the road surface4 ,it is customary and highly desirable that the general nature and extent of the improvement be established before the bonds are issued4 ,it is desirable that bond issues be subject to approval by referendum before issue and that is provided in every instance4 ,highway bonds are of three classes known as ,sinking ,fund1 ,annuity and ,serial ,bonds1 respectively4 ,the earlier bonds issued were almost all of the sinking fund class1 but in recent years the serial bond has been widely employed and is probably the most satisfactory to administer4 ,sinking ,fund ,bonds4#a--,when this type of bond is employed1 the amount of the expenditure for road improvement is determined upon and the length of the period during which tax payments shall be made is settled4 ,to employ a concrete example1 it may be assumed that #ajj1jjj is to be expended for road work and is to be paid at the end of ten years4 ,the interest rate on the bonds will vary with the condition of the bond market and the stability of the political unit issuing the bonds1 but is usually about #e per cent4 ,knowing these factors1 the amount to be added to the sinking fund each year is computed4 ,in order to pay the interest on the bonds1 a tax of suitable rate is levied1 and in order to retire the bonds at the end of the period1 a sum is set aside each year which is supposed to be invested and draw interest which will be added to the principle1 and the principle and interest comprise the sinking fund4 ,the principle of the sinking fund is obtained by tax levies1 a sum being added to the principle of the sinking fund each year4 #a ,for a more detailed discussion of highway bonds see ,bulletin #acf1 ,u4 ,s4 ,dept4 of ,agriculture1 which is the basis of this discussion4 ,the success of this method of financing depends upon the proper administration of the sinking fund4 ,it must be invested with fidelity and the fund be kept intact4 ,usually the sinking fund cannot be invested at as high a rate of interest as the bonds bear and there is some loss as a result4 ,road bonds bearing #e per cent interest can usually be sold at par while the sinking fund will usually net about #c or #c-a_/b per cent interest4 ,the total cost of a bond issue will be greater by the sinking fund method than by either of the other methods described4 ,annuity ,bonds4--,annuity bonds are drawn in such a manner that the amount of the payment for principle and interest is the same each year during the life of the bond4 ,when the amount of the issue and the rate of interest has been determined and the amount of the desired annual payment has been determined1 the number of years the bonds must run is computed4 ,this method is convenient in that the amount of the tax to be levied each year remains constant4 ,serial ,bonds4--,serial bonds are drawn so that a uniform amount of the principle is retired each year after retirement starts and the total interest payments decrease each year after the first bonds are retired4 ,the first bond may not be retired for a number of years after the issue of the bonds1 but when it once starts retirement proceeds at a constant rate annually4 ,comparison of ,methods of ,issuing ,bonds4--,the relative costs of financing by either of the three methods depends upon the rate of interest in each case and the net rate secured on the sinking fund provided for retiring sinking fund bonds4 ,for comparative purposes1 some typical examples are given in ,table #c4 ,these illustrate the differences in total cost of securing #ajj1jjj by each of the three methods at various interest rates4 ,,table #c ,,total ,,cost ,,of ,a ,,loan ,,of #ajj1jjj ,,for #bj ,,years1 ,,interest ,,compounded ,,annually ---------------------------------------- -------------------------- ,annual ,sinking ,fund ,compounded ,interest ,annually at on ,bonds ------------------------------------- ,annuity ,serial #c per cent #c-a_/b per cent #d per cent ---------------------------------------- ------------------------ #d #aed1dca #aej1gbb #adg1afc #adg1afc #adb1jjj #d-a_/b #afd1dca #afj1gbb #aeg1afc #aec1geb #adg1bej #e #agd1dca #agj1gbb #afg1afc #afj1dhe #aeb1ejj #e-a_/b #ahd1dca #ahj1gbb #agg1afc #afg1cei #aeg1gej #f #aid1dca #aij1gbb #ahg1afc #agd1cfi #afc1jjj ---------------------------------------- ------------------------ ,desirability of ,road ,bonds4--,in theory the bond method of financing enables the highway authorities to construct a large mileage of roads in a few years and spreads the cost over the period during which the public is being benefited4 ,better prices are obtained on contracts for a large mileage than for smaller jobs1 and the community can receive the benefit more quickly than where construction proceeds piecemeal with current funds4 ,the vital consideration is to insure that the term of the bonds is well within the useful life of the road1 and that ample provision is made to maintain the roads during that period4 ,under proper restrictions the bond method of financing is to be commended4 ,the bonds are an attractive investment and readily marketable on satisfactory terms4 ,,chapter ,,iii ,,drainage ,,of ,,roads ,the ,necessity for ,drainage4--,the importance of drainage for all roads subject to the effects of storm or underground water has always been recognized by road builders1 but during recent years constantly increasing attention has been given to this phase of road construction4 ,it is unfortunate that there has in the past been some tendency to consider elaborate drainage provisions less necessary where rigid types of surfaces were employed4 ,it has become apparent1 from the nature of the defects observed in all sorts of road surfaces1 that to neglect or minimize the importance of drainage in connection with either earth roads or any class of surfaced roads is to invite rapid deterioration of some sections of the roadway surface and to add to maintenance costs4 ,the degree to which lack of drainage provisions affect the serviceability of the road surface varies with the amount of precipitation in the locality and the manner in which it is distributed throughout the year4 ,in the humid areas of the ,united ,states1 which are1 roughly1 those portions east of a north and south line passing through ,omaha and ,kansas ,city1 together with the northern part of the ,pacific slope1 precipitation is generally in excess of #cj inches per year and fairly well distributed throughout the year1 but with seasonal variations in rate4 ,in these areas1 the effect of the precipitation1 both as regards its tendency to lower the stability of soils and as an eroding agent1 must be carefully provided against in highway design4 ,outside of the areas mentioned above1 the precipitation is much less than #cj inches per year and its effect as an agent of erosion is of greatest significance1 although in restricted areas there may be short periods when the soil is made unstable by ground water4 ,importance of ,design4--,the drainage system for a proposed road improvement ought to be designed with as much care as any other element1 and1 to do so1 a study must be made of all factors that have any bearing on the drainage requirements and the probable effectiveness of the proposed drainage system4 ,the well established principles of land drainage should be followed so far as applicable4 ,the basic principle of road drainage is to minimize the effect of water to such an extent that there will always be a layer of comparatively dry soil of appreciable thickness under the traveled part of the road4 ,this layer should probably never be less than two feet thick and for soils of a structure favorable to capillary action it should be at least three feet thick4 ,the means employed to accomplish the requisite drainage will be as various as the conditions encountered4 ,surface ,drainage4--,the drainage method which is by far the most nearly general in application is that which utilizes open ditches1 and the system which employs these ditches is usually referred to as surface drainage4 ,the full possibilities of this method of minimizing the effects of storm water are rarely fully utilized in road construction4 ,very frequently1 deterioration of a road surface is directly attributable to failure to provide adequately for the removal of the storm water or water from the melting of snow that has fallen on the road1 or water that flows to the road from land adjacent thereto4 ,surface water can usually most cheaply and expeditiously be carried away in open ditches1 although special conditions are occasionally encountered which require supplementary tile drains4 ,the cross section commonly adopted for roads lends itself naturally to the construction of drainage ditches at the sides of the traveled way1 and these are usually the principal dependence for the disposal of storm water4 ,run-off4--,the capacity required of side ditches to insure satisfactory surface drainage will be affected by the amount and nature of the precipitation in the region where the road is built4 ,the annual rainfall in a region may amount to several feet1 but may be well distributed throughout the year with an absence of excessive rainfall for short periods1 that is1 flood conditions may rarely occur4 ,in other areas1 the annual rainfall may be comparatively small but the precipitation occurs at a very high rate1 that is1 flood conditions may be common1 or it may be at a low rate extending over a considerable period4 ,these peculiarities must be known before an adequate drainage system can be planned4 ,it is almost universally true in the ,united ,states that precipitation at a very high rate will be for a relatively short duration1 and during these short periods1 which usually do not exceed thirty minutes1 a portion of the water that falls on the areas adjacent to the road and that drains to the road ditches will soak into the soil and therefore not reach the ditches along the road4 ,the extent to which the water is taken up by the soil will vary with the porosity and slope of the land and the character of the growth thereon4 ,cultivated land will absorb nearly all of the water from showers up to fifteen or twenty minutes duration2 grass land a somewhat smaller percentage2 and hard baked or other impervious soil will absorb a comparatively small amount4 ,rocky ground and steep slopes will absorb very little storm water4 ,the surface of the road is designed to turn water rapidly to the ditches1 but when the material is the natural soil1 there is always considerable absorption of storm water4 ,surfaces such as sandclay1 gravel and macadam do not absorb to exceed #aj per cent of the precipitation during short showers4 ,bituminous surfaces1 brick and concrete pavements1 do not absorb an appreciable amount of storm water4 ,generally it is best to assume that if a rain lasts for forty-five minutes or more1 all of the water will run off1 as the soil will reach a state of saturation in that time4 ,this is not true of deep sand1 but is for nearly all other soils4 ,the ditch capacity needed will therefore depend upon the area drained1 the character of the soil1 the slopes and the rainfall characteristics of the region1 and upon the nature of the road surface4 ,for a required capacity1 the cross section area of the ditch will vary inversely as the grade1 because the velocity of flow increases with an increase in the grade of the ditch4 ,if the surface water must be carried along the road for distances exceeding five or six hundred feet1 the ditch must be constructed of increasing capacity toward the outlet in order to accommodate the accumulated volume of water4 ,the velocity of flow varies not only with the grade1 but with the shape of the cross section1 cleanness of the channel1 the depth of the water in the channel1 alignment of the channel and the kind of material in which the channel is formed4 ,it is not necessary to go to great refinement in the design of the side ditches for the ordinary case where the water is carried along the road for only a few hundred feet4 ,the ditches are made of ample capacity by using the commonly accepted cross section for a road1 which will be discussed in a later paragraph4 ,but where large areas must be drained by the road ditches1 it is desirable carefully to design the side ditches4 ,the basis for that design is too lengthy to be included herein1 and reference should be made to a standard treatise on the subject4 ,ordinary ,design of ,ditches4--,for grades of one per cent or less on roads in the humid area1 the bottom of the ditch should be at least three and one-half feet lower than the traveled surface of the road1 except for very sandy soil4 ,for grades greater than one per cent1 this depth may be decreased one foot1 and for grades of four per cent and upward1 the depth may be still less4 ,these general rules for depth are susceptible of variation but are believed to be the minimum except in arid or semi-arid climates4 ,it is far better to be too liberal in ditch allowance than to be too conservative4 ,in arid or semi-arid regions1 the ditch design will be based on the necessity of providing for flood flow and preventing damage through erosion4 ,ordinary drainage requirements will be satisfactory with the ditch about one foot deep4 ,if the topography is such that it is evident considerable storm water will flow from the adjacent land to the road ditches1 the design must be modified to take this into account4 ,sometimes such water can be diverted by ditches well back from the road1 and thus prevented from flowing into the side ditches along the roadway4 ,it is especially desirable to divert water1 which would otherwise flow down the slope of a cut1 by means of a ditch on the hill-side above the upper edge of the slope of the cut4 ,ditches are not effective unless they afford a free flow throughout their length and have an outlet to a drainage channel of ample capacity4 ,therefore1 ditch grades should be established by survey1 especially if the gradient is less than one per cent1 and the construction work should be checked to insure that the ditch is actually constructed as planned4 ,a few high places in the ditch will greatly reduce the effectiveness1 although these may appear at the time of construction to be slight4 ,constricted places1 such as might be due to a small amount of loose earth left in the ditch1 are always to be avoided4 ,where the side ditch passes from a cut to the berm alongside a fill1 the ditch should be excavated throughout in the undisturbed natural soil1 five feet or more from the toe of the slope of the fill1 and along the filled portion of the road there should be a berm of three or four feet between the toe of the slope of the fill and the near edge of the ditch4 ,underground ,water4--,in a preceding paragraph1 mention was made of the fact that only a part of the storm water runs off over the surface of the ground1 the larger part being absorbed by the soil4 ,the water thus absorbed flows downward through the pores in the soil until it is deflected laterally by some physical characteristic of the soil structure4 ,the movement of underground water is affected by many circumstances1 but only two conditions need be discussed herein4 ,underground water1 like surface water1 tends to attain a level surface1 but in so doing it may need to flow long distances through the pores of the soil1 and to overcome the resistance incident to so doing some head will be required4 ,that is to say1 the water will be higher at some places than at others4 ,if a cut is made in grading the road1 the road surface may actually be lower than the ground water level in the land adjoining the road4 ,as a result1 the water will seep out of the side slopes in the cut and keep the ditches wet1 or even furnish enough water to occasion a flow in the ditch4 ,similarly1 the higher head of the underground water near the top of a hill may result in ground water coming quite close to the surface some distance down the hill4 ,the remedy in both cases is tile underdrains alongside the road to lower the ground water level so that it cannot affect the road surface4 ,sometimes the ground water encounters an impervious stratum as it flows downward through the soil1 or one that is less pervious than the surface soil4 ,when such is the case1 the water will follow along this stratum1 and should there be an outcrop of the dense stratum1 a spring will be found at that place4 ,this may be on a highway4 ,the impervious stratum may not actually outcrop but may lie only a few feet under the surface of the road1 in which case1 the road surface will be so water soaked as to be unstable4 ,the so-called seepy places so often noted along a road are generally the result of this condition4 ,this condition can be corrected by tile laid so as to intercept the flow at a depth that precludes damage to the road4 ,commonly1 the tile will be laid diagonally across the road some distance above the section where the effect of the water is noted1 and will be turned parallel to the road at the ditch line and carried under one of the side ditches to an outlet4 ,tile ,drains4--,where the soil and climatic conditions are such that the roadway at times becomes unstable because of underground water rising to a level not far below the road surface1 the ground water level is lowered by means of tile underdrains4 ,the function of the tile drains in such cases is precisely the same as when employed in land drainage2 to lower the ground water level4 ,laying ,tile4--,the tile lines are usually laid in trenches parallel to the center line of the road near the ditch line and at least #d feet deep so as to keep the ground water level well down4 ,they must be carefully laid to line and grade4 ,a good outlet must be provided and the last few joints of pipe should be bell-and-spigot sewer pipe with the joints filled with cement mortar4 ,the opening of the tile should be covered with a coarse screen to prevent animals from nesting in the tile4 ,it is frequently necessary to lay a line of tile at the toe of the slope in cuts to intercept water that will percolate under the road from the banks at the sides4 ,in some cases1 it is desirable to back-fill the tile trench with gravel or broken stone to insure rapid penetration of surface water to the tile4 ,in other instances1 it is advantageous to place catch basins about every three or four hundred feet4 ,these may be of concrete or of tile placed on end or may be blind catch basins formed by filling a section of the trench with broken stone4 ,when a blind catch basin is used1 the top should be built up into a mound1 and for a tile or concrete catch basin1 a grating of the beehive type should be used1 so that flow to the tile will not be obstructed by weeds and other trash that is carried to the catch basin4 ,culverts4--,culverts and bridges are a part of the drainage system and the distinction between the two is merely a matter of size4 ,generally1 structures of spans less than about eight feet are classed as culverts1 but the practice is not uniform4 ,in this discussion culverts will be defined as of spans of #h feet or less4 ,numerous culverts are required to afford passage for storm water and small streams crosswise of the road1 and their aggregate cost is a large item in the cost of road improvement4 ,the size of the waterway of a culvert required in any location will be estimated by an inspection of the stream and existing structure1 and by determining the extent and physical characteristics of the drainage area4 ,sometimes there is sufficient evidence at the site to indicate quite closely the size required1 but this should always be checked by run-off computations4 ,the drainage area contributing water to the stream passing through the culvert under consideration is computed from contour maps or from a survey of the ground1 and the size of culvert determined by one of the empirical formulas applicable to that purpose4 ,in these formulas1 the solution depends upon the proper selection of a factor ,c which varies in accordance with the nature of the drainage area4 ,two of these that are quite widely used are as follows3 ,myers' ,formula3 a ,,ca ,where a area of cross section of culvert in square feet4 ,a area in acres of the drainage area above culvert4 ,c a factor varying from #a for flat country to #d for mountainous country or rocky soil1 the exact value to be selected after an inspection of the drainage area4 ,talbot's ,formula3 ,area of waterway in square feet ,c ,square root of 77,drainage area in acres7#c7 ,transcriber's ,note3 ,the above formula used the mathematical square root symbol in the original4 ,one should read it as ,c times the square root of the ,drainage area in acres cubed4 ,c being variable according to circumstances thus3 ,for steep and rocky ground ,c varies from #b_/c to #a4 ,for rolling agricultural country1 subject to floods at times of melting snow1 and with length of valley three or four times its width1 ,c is about #a_/c1 and if stream is longer in proportion to the area1 decrease ,c4 ,in districts not affected by accumulated snow1 and where the length of valley is several times its width1 #a_/e or #a_/f or even less may be used4 ,c should be increased for steep side slopes1 especially if the upper part of the valley has a much greater fall than the channel at the culvert4 ,the value of ,c to be used in any case is determined after an inspection of the drainage area4 ,illustration3 ,fig4 #b4 ,design of ,pipe ,culvert and ,bulkhead ,length of ,culvert4--,the clear length between end walls on a culvert should be at least equal to the width of the roadway between ditches4 ,this is a minimum of #bj feet for secondary roads and ranges from #bd to #cj feet for main roads4 ,the headwall to the culvert should not be a monument1 but should be no higher than needed to prevent vehicles from leaving the roadway at the culvert4 ,farm ,entrance ,culverts4--,at farm entrances1 culverts are required to carry the farm driveway across the side ditch of the road4 ,these culverts are usually about #af feet along1 and should be of a size adequate to take the flow of the side ditch4 ,the farm entrance culvert should be of such design that it can be easily removed to permit cleaning out the ditches with a road grader4 ,,types ,,of ,,culverts ,culverts constructed of concrete and poured in place are called box culverts because of the rectangular form of the cross section4 ,culverts of pre-cast pipe are known as pipe culverts4 ,several forms of pipe culvert are in general use4 ,illustration3 ,fig4 #c4--,typical ,concrete ,box ,culvert ,metal ,pipe4--,these may be of cast iron1 steel or wrought iron4 ,the cast iron pipe is very durable but expensive and heavy to handle and is not widely used in highway construction4 ,steel pipe has been employed to a limited extent but its durability is questioned4 ,at least it is known that the pipe made from uncoated1 light sheet steel is not very durable4 ,sheet iron and sheets made from alloy iron coated with spelter have been extensively used and seem to be durable1 especially when laid deep enough to eliminate possibility of damage from heavy loads4 ,to insure reasonable resistance to corrosion1 the metal sheets should be coated with at least one and one-half ounces of spelter per square foot of sheet and the sheets should not be lighter than #af gauge for small sizes and should be heavier for the larger sizes4 ,clay and ,cement ,concrete ,pipe4--,the ordinary burned clay bell and spigot pipe that is employed for sewer construction is sometimes used for culverts4 ,it must be very carefully bedded1 preferably on a concrete cradle and the joints filled with cement mortar4 ,culverts of this type have a tendency to break under unusual loads1 such as traction engines or trucks4 ,they may be damaged by the pressure from freezing water1 particularly when successive freezing and thawing results in the culvert filling with mushy snow1 which subsequently freezes4 ,concrete ,pipe4--,reinforced concrete pipe is a satisfactory material for culverts1 if the pipe is properly designed4 ,the pipe should be carefully laid on a firm earth bed with earth carefully back-filled and tamped around the pipe4 ,the joints in the pipe should be filled with cement mortar1 or should be of a design that will be tight4 ,endwalls for ,culverts4--,a substantial retaining wall is placed at each end of the culvert barrel1 whatever the type4 ,this is to prevent the end of the culvert from becoming choked with earth and to retain the roadway at the culvert4 ,it also indicates to the drivers the location of the end of the culvert4 ,the endwall extends a foot or more below the floor of the culvert to prevent water from cutting under the barrel4 ,plain concrete or stone masonry are most commonly used for culvert endwalls4 ,illustration3 ,fig4 #d4--,two ,types of ,drop ,inlet ,culvert ,reinforced ,concrete ,box ,culverts4--,the pipe culvert is limited in application to the smaller waterways4 ,reinforced concrete is extensively used for culverts of all sizes1 but especially for the larger ones4 ,these are usually constructed with endwalls integral with the barrel of the culvert4 ,culverts of this type must be designed for the loads anticipated to insure suitable strength and stability1 and must be constructed of a good quality of concrete4 ,figs4 #b and #c show designs for pipe and box culverts4 ,illustration3 ,fig4 #e4--;,drop ,inlet ,culvert ,drop ,inlet ,culverts4--,in some locations erosion has begun in the fields adjacent to a culvert and it will probably continue until the stream above the culvert has eroded to about the level of the floor of the culvert4 ,this is a reason for placing the culvert as high as the roadway will permit1 so long as the area above the culvert will be properly drained4 ,considerable reclamation of land is possible if the culvert is constructed with a box at the inlet and as shown in ,fig4 #d4 ,the area up-stream from the culvert will not erode below the level of the top of the box at the inlet end4 ,where the stream crossing the road has eroded to considerable depth or has considerable fall1 as would sometimes be the case on side hill roads1 the culvert barrel would follow the general slope of the ditch but should have a drop inlet4 ,this type of culvert is shown in ,fig4 #e4 ,,chapter ,,iv ,,road ,,design ,necessity for ,planning4--,sometimes highway improvement is the result of spasmodic and carelessly directed work carried out at odd times on various sections of a road1 finally resulting in the worst places being at least temporarily bettered4 ,the grade on the steepest hills is probably reduced somewhat and some of the worst of the low lying sections are filled in and thereby raised4 ,short sections of surfacing such as gravel or broken stone may be placed here and there4 ,from the standpoint of the responsible official1 the road has been improved1 but too often such work does not produce an improvement that lasts1 and sometimes it is not even of any great immediate benefit to those who use the roads4 ,in nearly every instance such work costs more in money and labor that it is worth4 ,lasting improvement of public highways can be brought about only through systematic and correlated construction carried on for a series of years4 ,in other words1 there must be a road improvement policy which will be made effective through some agency that is so organized that its policies will be perpetuated and is clothed with enough authority to be capable of enforcing the essential features of good design and of securing the proper construction of improvements4 ,details of highway construction and design must vary with many local conditions and types of surface4 ,the limits of grades and the many other details of design may properly be adopted for a specific piece of work only after an adequate investigation of the local requirements and in the light of wide experience in supervising road improvement4 ,new ideas are constantly being injected into the art of road building1 but these are disseminated somewhat slowly1 so that valuable devices and improvements in methods remain long unknown except to the comparatively few who have the means for informing themselves of all such developments4 ,it follows then that the logical system of conducting road improvement is through an agency of continuing personnel which will supervise the preparation of suitable plans and direct the construction in accordance with the most recent experience4 ,road ,plans4--,the information shown on the plans prepared for road improvement varies somewhat with the design and with the ideas of the engineer as to what constitutes necessary information1 but in general the plans show the existing road and the new construction contemplated in an amount of detail depending principally upon the character of the construction4 ,simple plans suffice for grade reduction or reshaping an earth road surface1 while for the construction of paved roads1 the plans must be worked out in considerable detail4 ,the essential requirement is that there be given on the plans all information necessary to enable the construction to be carried out according to the intentions of the engineer1 that all parts of the work fit together1 that the culverts are of the proper size and located at the proper places1 ditches drain properly1 grades are reduced to the predetermined rate1 that excavated material is utilized and that an exact record of the work done is retained4 ,plans are indispensable to economical road construction and the preparation of the plans is the work of the expert in road design1 that is1 the highway engineer4 ,problem of ,design4--,the problem of road design is to prepare plans for a road improvement with the various details so correlated as to insure in the road constructed in accordance therewith the maximum of safety1 convenience and economy to the users thereof4 ,the degree to which the design will be effective will depend to a considerable extent upon the financial limitations imposed upon the engineer1 but skill and effort on the plans will do a great deal to offset financial handicap and no pains should be spared in the preparation of the plans4 ,moreover1 the plans must afford all of the information needed by the contractor in preparing a bid for the work4 ,preliminary ,investigation4--,the first step in road improvement is to secure an adequate idea of the existing conditions on the road or roads involved4 ,the detail to which this information need go will depend entirely upon the purpose of the preliminary investigation1 for before a definite plan is prepared1 it may be necessary to choose the best from among several available routes4 ,for this purpose1 it is not always necessary to make an actual instrument survey of the several routes4 ,a hasty reconnaissance will usually be sufficient4 ,this is made by walking or riding over the road and noting1 in a suitable book or upon prepared blanks1 the information needed4 ,the items of information recorded will usually be as follows3 distances1 grades1 type of soil on the road and nature of existing surface1 character of drainage1 location of bridges and culverts and the type of each with notes as to its condition1 location of railway crossings and notes as to type1 location of intersecting roads1 farm entrances1 and all similar features that have a bearing on the choice of routes4 ,these data can be obtained in a comparatively short time by a skilled observer who may drive over the road in a motor car4 ,sometimes it may be desirable to make a more careful study of some certain sections of road and this may be done by waking over the section in question in order to make a more deliberate survey of the features to be considered than is possible when riding in a motor car4 ,factors other than relative lengths of routes will obviously determine the cost of improvement and the comparative merits of the improved roads4 ,some special characteristic of a road1 such as bad railroad crossings or a few bad hills1 may eliminate a route1 or availability of materials along a route may offset disadvantages of alignment or grade4 ,in special cases1 complete surveys of routes may be required finally to select the best route1 but these instances are few in number4 ,road ,surveys4--,when a road has been definitely selected for improvement1 a careful survey is made to furnish information for the preparation of the plans4 ,this will consist of a transit survey and a level survey4 ,the transit survey is made by running a line between established corners following the recorded route of the road1 or if no records are available or the road is irregular in alignment1 by establishing arbitrary reference points and running a line along the center line of the existing road or parallel thereto4 ,the topography is referenced to this line in such completeness that it can be reproduced on the plans4 ,the level survey consists in taking levels on cross sections of the road at one hundred foot intervals1 and oftener if there are abrupt changes in grade4 ,special level determinations are made at streams1 railroad crossings1 intersecting roads or lanes and wherever it appears some special features of the terrain should be recorded4 ,from the surveys and such other information as has been assembled relative to the project1 a plan is prepared which embodies a design presumed to provide for an improvement in accordance with the best highway practice4 ,,the ,,problem ,,of ,,design ,it will be convenient to consider separately the components of a road design1 although in the actual design the consideration of these cannot be separated because all parts of the plan must fit together4 ,alignment4--,the alignment of the road is determined to a considerable extent by the existing right-of-way1 which may follow section lines1 regardless of topography1 as is the case with many roads in the prairie states1 or it may follow the valleys1 ridges1 or other favorable location in hilly country4 ,in many places the roads of necessity wind around among the hills in order to avoid excessive grades4 ,in designing an improvement1 it is generally desirable to follow the existing right-of-way so far as possible4 ,but the element of safety must not be lost sight of1 and curves should not preclude a view ahead for sufficient distance to insure safety to vehicles4 ,the necessary length of clear view ahead is usually assumed to be #bej feet1 but probably #bjj feet is a satisfactory compromise distance when a greater distance cannot be obtained at reasonable cost4 ,to secure suitable sight distance1 the curves must be of long radii1 and where possible the right-of-way on the inside of the curve should be cleared of trees or brush that will obstruct the view4 ,where the topography will not permit a long radius curve and the view is obstructed by an embankment or by growing crops or other growth1 it is desirable to separate the tracks around the curve to eliminate the possibility of accidents on the curve4 ,this is readily accomplished if the road is surfaced1 but if it is not surfaced1 the same end is accomplished by making the earth road of ample width at the curve4 ,relocations should be resorted to whenever they shorten distances or reduce grades sufficiently to compensate for the cost4 ,intersections4--,at road intersections1 it is always difficult to design a curve that entirely meets the requirements of safety because there is not enough room in the right-of-way1 and enough additional right-of-way must be secured to permit the proper design4 ,it is not necessary to provide an intersection that is adapted to high speed traffic1 where main roads cross1 but1 on the contrary1 a design that automatically causes traffic to slow up has distinct advantages4 ,where a main route1 improved with a hard surface1 crosses secondary roads1 it is satisfactory to continue the paved surface across the intersecting road at normal width and make no provision for the intersecting road traffic other than a properly graded approach at the intersection4 ,superelevation4--,on all curved sections of road1 other than intersections1 account is taken of the tendency of motor cars to skid toward the outside of the curve4 ,this tendency is counteracted by designing the cross section with superelevation4 ,illustration3 ,fig4 #f ,in ,fig4 #f1 ,f represents the tangential force that tends to cause skidding4 ,w represents the weight of the vehicle in pounds1 ,,theta the angle of superelevated surface c-d1 with the horizontal c-a4 ,r represents the radius of the curve upon which the vehicle is moving4 w is the component of the weight parallel to the surface c-d1 v velocity of the vehicle in feet per second4 m mass of vehicle ,w_/g ,,theta w ,w tan ,,theta mv#b wv#b ,f ------- ------ ,r g,r ,if ,f w there will be no tendency to skid2 hence the rate of superelevation necessary in any case is as follows3 ,wv#b ,w tan ,,theta ------- g,r v#b tan ,,theta ------- g,r ,the amount of superelevation required1 therefore1 varies as the square of the velocity and inversely as the radius of the curve4 ,theoretically1 the amount of the superelevation should increase with a decrease in the radius of the curve and should also increase as the square of the speed of the vehicle4 ,on account of the variation in speeds of the vehicles1 the superelevation for curves on a highway can only be designed to suit the average speed4 ,at turns approaching ninety degrees1 the curve is likely to be of such short radius that it is impossible to maintain the ordinary road speed around the curve1 even with the maximum superelevation permissible4 ,it is good practice to provide the theoretical superelevation on all curves having radii greater than #cjj feet for vehicle speeds of the maximum allowed by law1 which is generally about #be miles per hour4 ,where the radii are less than #cjj feet1 the theoretical superelevation for the maximum vehicle speeds gives a superelevation too great for motor trucks and horse drawn vehicles and generally no charge is made in superelevation for radii less than #cjj feet1 but all such curves are constructed with the same superelevation as the curve with #cjj foot radius4 ,the diagram in ,fig4 #g shows the theoretical superelevation for various curve radii4 ,illustration3 ,fig4 #g4 ,curves showing ,theoretical ,superelevation for ,various ,degrees of ,curve for ,various ,speeds of ,vehicle ,at the intersection of important highways1 the problem is complicated by the necessity for providing for through traffic in both directions and for traffic which may turn in either direction and the engineer must provide safe roadways for each class of traffic4 ,tractive ,resistance4--,the adoption of a policy regarding the grades on a road involves an understanding of the effect of variation in the character of the surface and in rate of grade upon the energy required to transport a load over the highway4 ,the forces that oppose the movement of a horse drawn vehicle are fairly well understood and their magnitude has been measured by several observers1 but comparatively little is known about the forces opposing translation of rubber tired self-propelled vehicles4 ,the resistance to translation of a vehicle is made up of three elements3 resistance of the road surface to the rolling wheel1 resistance of the air to the movement of the vehicle and internal friction in the vehicle itself4 ,rolling ,resistance4--,when the wheel of a vehicle rolls over a road surface1 both the wheel and the surface are distorted4 ,if the wheel has steel tires and the road surface is plastic1 there will be considerable distortion of the road surface and very little of the wheel4 ,a soft rubber tire will be distorted considerably by a brick road surface4 ,between these extremes there are innumerable combinations of tire and road surface encountered1 but there is always a certain amount of distortion of either road surface or wheel1 or of both1 which has the same effect upon the force necessary for translation as a slight upward grade4 ,when both the tire and the road surface strongly resist distortion 7as steel tires on vitrified brick paving71 the resistance to translation is low but the factor of impact is likely to be introduced4 ,where impact is present1 energy is used up in the pounding and grinding of the wheels on the surface1 and this factor increases as the speed of translation1 and may be a considerable item4 ,impact is especially significant on rough roads with motor vehicles1 particularly trucks1 traveling at high speed4 ,these two factors 7impact and rolling resistance7 combined constitute the major part of the resistance to translation for horse drawn vehicles4 ,internal ,resistance4--,for horse drawn vehicles1 the internal resistance consists of axle friction1 which is small in amount4 ,for self-propelled vehicles1 the internal resistance consists of axle friction and friction in the driving mechanism1 of which gear friction and the churning of oil in the gear boxes is a large item4 ,internal friction is of significance in all self-propelled vehicles and especially so at high speeds4 ,air ,resistance4--,at slow speeds1 the resistance of still air to translation is small1 but as the speed increases1 the air resistance increases rapidly and at the usual speed of the passenger automobile on the road becomes a very considerable part of the total resistance to translation4 ,this factor has no significance in connection with horse drawn vehicles1 but is to be taken into account when dealing with self-propelled vehicles at speeds in excess of five miles per hour4 ,many determinations of tractive resistance with horse drawn vehicles have been made from time to time and these show values that are fairly consistent when the inevitable variations in surfaces of the same type are taken into account4 ,table #d is a composite made up of values selected from various reliable sources and ,table #e is from experiments by ,professor ,j4 ,b4 ,davidson on ,california highways4 ,,table #d ,,average ,,tractive ,,resistance ,,of ,,road ,,surfaces ,,to ,,steel ,,tired ,,vehicles ,surface ,tractive force per ton ,earth packed and dry #ajj ,earth dusty #ajf ,earth muddy #aij ,sand loose #cbj ,gravel good #ea ,gravel loose #adg ,cinders well-packed #ib ,oiled road--dry #fa ,oiled road--wet #ajh ,macadam--very good #ch ,macadam--average #df ,sheet asphalt #ch ,asphaltic concrete #dj ,vitrified brick--new #ef ,wood block--good #cc ,wood block--poor #db ,cobblestone #ed ,granite tramway #bg ,asphalt block #eb ,granite block #dg ,,table #e ,,tractive ,,resistances ,,to ,,steel ,,tired ,,vehicles#a ---------------------------------------- -------------------------- ,condition ,tractive ,resistance ,test ,no4 ,kind of ,road of ,road ,total lb4 per ton lb4 ---------------------------------------- -------------------------- #bi-cj-ca ,concrete ,good1 excellent #hc4j #bg4f 7unsurfaced7 #baa-ab ,concrete ,good1 excellent #ij4j #cj4j 7unsurfaced7 #bf-bg-bh ,concrete #c_/h-;in4,good1 excellent #adg4f #di4b surface asphaltic oil and screenings #ac-ad ,concrete #c_/h-;in4,good1 excellent #aee4j #ea4f surface asphaltic oil and screenings #i-aj ,macadam1 ,good1 excellent #aic4j #fd4c water-bound #bb-bc ,topeka on ,good1 excellent #bje4e #fh4e concrete #h ,gravel ,compact1 good #bbe4j #ge4j condition #cde-dh ,oil macadam ,good1 new #bcd4e #gh4b #ddf-dg ,oil macadam ,good1 new #bdd4j #ha4c #ch ,gravel ,packed1 in #bdg4j #hb4c good condition #ah-ai-bj ,topeka on plank ,good condition1 #bfe4j #hh4c soft1 wagon left marks #cd ,earth road ,firm1 #a-a_/b-;in4 #bgf4j #ib4j fine loose dust #bd-be ,topeka on plank ,good condition1 #bgh4j #ib4f but soft #a-b-e ,earth road ,dust #c_/d to #b in4 #bih4j #ii4c #c-c ,earth ,mud1 stiff1 firm #fed4j #bah4j underneath #f-g ,gravel ,loose1 not packed #ghi4j #bfc4j ---------------------------------------- -------------------------- #a ,prof4 ,j4 ,b4 ,davidson in ,engineering ,news-,record1 ,august #ag1 #aiah4 #b ,graphic record indicates that the load was being accelerated when test was started4 #c ,drawn with motor truck at #b-a_/b miles per hour4 #d ,drawn with motor truck at #e miles per hour4 ,comparatively few data are available showing the tractive resistance of motor vehicles1 but the following tables are based on sufficient data to serve to illustrate the general trend4 ,these data on the tractive resistances of an electric truck with solid rubber tires on asphalt and bitulithic1 wood1 brick and granite block1 water-bonded and tar macadam1 cinder and gravel road surfaces were obtained by ,a4 ,e4 ,kennelly and ,o4 ,r4 ,schurig in the research division of the electrical engineering department of the ,massachusetts ,institute of ,technology1 and are published in ,bulletin ,no4 #aj of the division4 ,an electric truck was run over measured sections1 ranging from #djj to #bfjj feet in length1 surfaced with these various materials1 at certain speeds per hour1 ranging from about #h to about #ae4e miles per hour4 ,the result of the observations of speeds1 tractive resistances1 conditions of surfaces1 etc41 were collected and studied in various combinations4 ,,table #f ---------------------------------------- -------------------------- ,tractive ,tractive ,resistance ,resistance ,type of ,surface ,condition of ,surface in lbs4 in lbs4 per ton per ton #aj miles #ab4d miles per hr4 per hr4 ---------------------------------------- -------------------------- ,asphalt ,good #bj4d ,asphalt ,poor #bb4f #be4e ,wood block ,good #bd4b #be4c ,brick block ,good #bd4f #bf4f ,granite block ,good #dj4c #de4ge ,brick block ,slightly worn #be4a #bh4j ,granite block with cement joints ,good #be4e #cj4b ,macadam1 water bonded ,dry and hard #bc4c #be4h ,macadam1 water bonded ,fair1 heavily oiled #ce4i #ch4g ,macadam1 water bonded ,poor1 damp1 some holes #cf4c #da4f ,tar macadam ,good #be4g #bh4j ,tar macadam ,very soft #cf4h #ch4g ,tar macadam ,many holes1 soft1 extremely poor #eb4d #fj4f ,cinder ,fair1 hard #bg4e #cj4f ,gravel ,fair1 dusty #cj4d #cc4j ---------------------------------------- -------------------------- ,illustration3 ,fig4 #h ,effect of ,grades4--,grades increase or decrease the resistance to translation due to the fact that there is a component of the weight of the vehicles parallel to the road surface and opposite in direction to the motion when the load is ascending the hill and in the same direction when the vehicle is descending4 ,in ,fig4 #h ,w represents the weight of the vehicle1 acting vertically downward1 w is the component of the weight perpendicular to the road surface and ,w#b is the component parallel to the road surface4 ,w#b ,w tan ,,theta4 tan ,,theta #j4ja per cent of grade4 ,w#b #j4ja ,w per cent grade4 ,w#b #j4ja #bjjj per cent of grade1 for each ton of weight of vehicle4 ,hence ,w#b #bj lbs4 per ton of load for each one per cent of grade4 ,the gravity force acting upon a vehicle parallel to the surface on a grade is therefore #bj lbs4 per ton for each one per cent of grade and this force tends either to retard or to accelerate the movement of the vehicle4 ,let ,f the sum of all forces opposing the translation of a vehicle4 ,f fr fi fp fa fg 7#a7 where fr rolling resistance of road surface4 fi resistance due to internal friction in the vehicle4 fp resistance due to impact of the road surface4 fa resistance due to air4 fg resistance due to grade1 which is positive when ascending and negative when descending4 ,all of the above in pounds per ton of #bjjj lbs4 ,let ,t the tractive effort applied to the vehicle by any means4 ,t must be greater than ,f in order to move the vehicle4 ,by an inspection of 7#a71 it will be seen that for a given vehicle and any type of road surface1 all terms are constant except fa and fg4 fa varies as the speed of the vehicle and the driver can materially decrease fa by reducing speed4 fg varies with the rate of grade4 ,for any vehicle loaded for satisfactory operation on a level road with the power available1 the limiting condition is the factor fg4 ,if the load is such as barely to permit motion on a level road1 any hill will stall the vehicle4 ,therefore1 in practice the load is always so adjusted that there is an excess of power on a level road4 ,if draft animals are employed the load is usually about one fourth of that which the animals could actually move by their maximum effort for a short period4 ,with motor vehicles1 the excess power is provided for by gearing4 ,if it be assured a load of convenient size is being moved on a level road by draft animals1 there is a limit to the rate of grade up which the load can be drawn by the maximum effort of the animals4 ,tests indicate that the horse can pull at a speed of #b-a_/b miles per hour1 an amount equal to #a_/h to #a_/aj of its weight1 and for short intervals can pull #c_/d of its weight4 ,the maximum effort possible is therefore six times the average pull1 but this is possible for only short intervals4 ,a very short steep hill would afford a condition where such effort would be utilized4 ,but for hills of any length1 that is1 one hundred feet or more but not to exceed five hundred feet1 it is safe to count on the draft animal pulling three times his normal pulling power for sustained effort4 ,the limiting grade for the horse drawn vehicle is therefore one requiring1 to overcome the effect of grade1 or fg1 a pull in excess of three times that exerted on the level4 ,a team of draft animals weighing #ahjj lbs4 each could exert a continuous pull of about #a_/aj of their weight or #cfj lbs4 ,if it be assumed that the character of the vehicle and the road surface is such that fr fi fp fa #ajj lbs4 per gross ton on a level section of road1 then the gross load for the team would be #c4f tons4 ,the same team could for a short time exert an additional pull of three times #cfj lbs4 or #ajhj lbs4 ,for each #a per cent of grade a pull of #bj lbs4 per ton would be required or fg for the #c4f tons load would be #gb lbs4 for each per cent of grade4 ,at that rate1 the limiting grade for the team would be fifteen per cent4 ,if1 however1 the character of the vehicle and the road surface were such that fr fi fp fa #fj lbs4 per gross ton on a level section of road1 the gross load for the team on the level would be #f tons1 and the limiting grade #i per cent4 ,the above discussion serves to illustrate the desirability of adopting a low ruling or limiting grade for roads to be surfaced with a material having low tractive resistance and the poor economy of adopting a low ruling grade for earth roads or roads to be surfaced with material of high tractive resistance4 ,it may be questioned whether horse drawn traffic should be the limiting consideration for main trunk line highways1 but it is certain that for a number of years horse drawn traffic will be a factor on secondary roads4 ,in the case of motor vehicles1 excess power is provided by means of gears and no difficulty is encountered in moving vehicles over grades up to #ab or #ae per cent1 so that any grade that would ordinarily be tolerated on a main highway will present no obstacle to motor vehicles1 but the economy of such design is yet to be investigated4 ,energy ,loss on ,account of ,grades4--,whether a vehicle is horse drawn or motor driven1 energy has been expended in moving it up a hill4 ,a part of this energy has been required to overcome the various resistances other than grade1 and that has been dissipated1 but the energy required to translate the vehicle against the resistance due to grade has been transformed into potential energy and can be partially or wholly recovered when the vehicle descends a grade1 provided the physical conditions permit its utilization4 ,if the grade is so steep as to cause the vehicle to accelerate rapidly1 the brakes must be applied and loss of energy results4 ,the coasting grade is dependent upon the character of the surface and the nature of the vehicle4 ,in the cases discussed in the preceding paragraph1 the coasting grades would be five per cent and three per cent respectively4 ,for horse drawn vehicles then the economical grades would be three and five per cent1 which again emphasizes the necessity of lower grades on roads that are surfaced than on roads with no wearing surface other than the natural soil4 ,the theory of grades is somewhat different when motor vehicles are considered1 since it is allowable to permit considerably higher speed than with horse drawn vehicles before applying the brakes and the effect of grade can be utilized not only in translating the vehicle down the grade1 but also in overcoming resistances due to mechanical friction and the air4 ,on long grades1 a speed might be attained that would require the use of the brake or the same condition might apply on very steep short grades4 ,there is at present insufficient data on the tractive resistance and air resistance with motor vehicles to permit the establishing of rules relative to grade1 but experience indicates a few general principles that may be accepted4 ,if a hill is of such rate of grade and of such length that it is not necessary to use the brake it may be assumed that no energy loss results so far as motor vehicles are concerned4 ,where there is no turn at the bottom of the hill and the physical condition of the road permits speeds up to thirty-five or forty miles per hour grades of five per cent are permissible if the length does not exceed five hundred feet and grades of three per cent one thousand feet long are allowable4 ,it is a rather settled conviction among highway engineers that on trunk line highways the maximum grade should be six per cent1 unless a very large amount of grading is necessary to reach that grade4 ,undulating ,roads4--,many hills exist upon highways1 the grade of which is much below the maximum permissible4 ,if there are grades ranging from #j to #d per cent1 with a few hills upon which it is impracticable to reach a grade of less than six per cent1 it is questionable economy to reduce the grades that are already lower than the allowable maximum4 ,it is especially unjustifiable to incur expense in reducing a grade from two per cent to one and one-half per cent on a road upon which there are also grades in excess of that amount4 ,the undulating road is not uneconomical unless the grades are above the allowable maximum or are exceptionally long or the alignment follows short radius curves4 ,safety ,considerations4--,on hills it is especially desirable to provide for safety and curves on hills are always more dangerous than on level sections of road4 ,therefore1 it is desirable to provide as flat grades as possible at the curves and to cut away the berm at the side of the road so as to give a view ahead for about three hundred feet4 ,whether a road be level or on a hill1 safety should always be considered and the most important safety precaution is to provide a clear view ahead for a sufficient distance to enable motor vehicle drivers to avoid accidents4 ,illustration3 ,fig4 #i4--,types of ,guard ,rails ,guard ,railing4--,when a section of road is on an embankment1 guard rails are provided at the top of the side slope to serve as warnings of danger1 and to prevent vehicles from actually going over the embankment in case of skidding1 or if for any reason the driver loses control4 ,these are usually strongly built1 but would hardly restrain a vehicle which struck at high speed4 ,but they are adequate for the protection of a driver who uses reasonable care4 ,a typical guard rail is shown in ,fig4 #i1 but many other designs of similar nature are employed4 ,at very dangerous turns a solid plank wall six or eight feet high is sometimes built of such substantial construction as to withstand the severest shock without being displaced4 ,trees1 shrubs and the berms at the side of the road in cuts are particularly likely to obstruct the view and should be cleared or cut back so far as is necessary to provide the proper sight distance4 ,width of ,roadway4--,for roads carrying mixed traffic1 #i feet of width is needed for a single line of vehicles and #ah feet for #b lines of vehicles4 ,in accordance with the above1 secondary roads1 carrying perhaps #be to #ej vehicles per day1 may have an available traveled way #ah feet wide4 ,those more heavily traveled may require room for three vehicles to pass at any place and therefore have an available traveled way #cj feet wide4 ,greater width is seldom required on rural highways1 and #bj feet is the prevailing width for main highways4 ,cross ,section4--,the cross section of the road is designed to give the required width of traveled way1 and1 in addition1 provide the drainage channels that may be needed4 ,in regions of small rainfall the side ditches will be of small capacity or may be entirely omitted1 but usually some ditch is provided4 ,the transition from the traveled way to ditch should be a gradual slope so as to avoid the danger incident to abrupt change in the shape of the cross section4 ,the depth of ditch may be varied without changing to width or slope of the traveled part of the road as shown in ,fig4 #aj4 ,illustration3 ,fig4 #aj ,control of ,erosion4--,the construction of a highway may be utilized to control general erosion to some extent1 particularly when public highways exist every mile or two and are laid out on a gridiron system1 as is the case in many of the prairie states4 ,the streams cross the highways at frequent intervals and the culverts can be placed so as effectually to prevent an increase in depth of the stream4 ,this will to some extent limit the erosion above the culvert and if such culverts are built every mile or two along the stream1 considerable effect is produced4 ,where small streams have their origin a short distance from a culvert under which they pass1 it is sometimes advisable to provide tile for carrying the water under the road1 instead of the culvert1 and1 by continuing the tile into the drainage area of the culvert1 eliminate the flow of surface water and reclaim considerable areas of land4 ,erosion in the ditches along a highway can be prevented by constructing weirs across the ditch at frequent intervals1 thus effectually preventing an increase in the depth of the ditch4 ,wherever water flows at a velocity sufficient to produce erosion or where the drainage channel changes abruptly from a higher to a lower level1 paved gutters1 tile or pipe channels should be employed to prevent erosion4 ,private ,entrances4--,entrance to private property along the highway is by means of driveways leading off the main road4 ,these should always be provided for in the design so as to insure easy and convenient access to the property4 ,the driveways will usually cross the side ditch along the road and culverts will be required to carry the water under the driveway4 ,driveways that cross a gutter by means of a pavement in the gutter are usually unsatisfactory1 and to cross the gutter without providing a pavement is to insure stoppage of the flow at the crossing4 ,the culvert at a driveway entrance must be large enough to take the ditch water readily or it will divert the water to the roadway itself4 ,generally end walls on such culverts are not required as in the case of culverts across a highway4 ,aesthetics4--,much of the traffic on the public highways is for pleasure and relaxation and anything that tends to increase the attractiveness of the highways is to be encouraged4 ,usually the roadside is a mass of bloom in the fall1 goldenrod1 asters and other hardy annuals being especially beautiful4 ,in some states wild roses and other low bushes are planted to serve the two-fold purpose of assisting to prevent erosion and to beautify the roadside4 ,in humid areas trees of any considerable size shade the road surface and are a distinct disadvantage to roads surfaced with the less durable materials such as sand-clay or gravel4 ,it is doubtful if the same is true of paved surfaces1 but the trees should be far enough back from the traveled way to afford a clear view ahead4 ,shrubs are not objectionable from any view-point and are to be encouraged for their beauty1 so long as they do not obstruct the view at turns4 ,,chapter ,v ,,earth ,,roads ,highways constructed without the addition of surfacing material to the natural soil of the right-of-way are usually called earth roads4 ,but if the natural soil exhibits peculiar characteristics or is of a distinct type1 the road may be referred to by some distinctive name indicating that fact4 ,hence1 roads are referred to as clay1 gumbo1 sandy or caliche roads as local custom may elect4 ,in each case1 however1 the wearing surface consists of the natural soil1 which may have been shaped and smoothed for traffic or may be in its natural state except for a trackway formed by the vehicles that have used it4 ,variations in ,soils4--,the nature of the existing soil will obviously determine the serviceability and physical characteristics of the road surface it affords4 ,that is to say that even under the most favorable conditions some earth roads will be much more serviceable than others1 due to the better stability of the natural soil4 ,some soils are dense and somewhat tough when dry and therefore resist to a degree the tendency of vehicles to grind away the particles and dissipate them in the form of dust4 ,such soils retain a reasonably smooth trackway in dry weather even when subjected to considerable traffic4 ,other soils do not possess the inherent tenacity and stability to enable them to resist the action of wheels and consequently grind away rapidly4 ,roads on such soils become very dusty4 ,these are the extremes and between them are many types of soils or mixtures of soils possessing varying degrees of stability1 and1 in consequence1 differing rates of wear4 ,similarly the various soils exhibit different degrees of stability when wet4 ,it is to be expected that soils will differ with the geographical location1 for it is well known that there is a great variation in soils in the various parts of the world4 ,but wide differences are also encountered in the soil on roads very near each other and even on successive stretches of the same road4 ,it is for this reason that earth roads often exhibit great differences in serviceability even in a restricted area4 ,variation in ,rainfall4--,the stability of a soil and its ability to support the weight of vehicles varies greatly with the amount of water in the soil4 ,a certain small amount of moisture in the soil is beneficial in that practically every soil compacts more readily when moist than when dry because the moisture aids in binding together the particles4 ,but most soils also become unstable when the amount of water present is in excess of that small amount referred to above and the stability decreases very rapidly as the amount of water in the soil increases4 ,the serviceability of an earth road will change continually as the moisture content of the soil changes and consequently the general utility of the earth road system in any locality is dependent to a considerable extent upon the amount and seasonal distribution of precipitation4 ,the methods of maintaining earth roads appropriate to any locality must of necessity be adapted to the climatic conditions1 and the amount of work required to give the highest possible degree of serviceability will be exceedingly variable from season to season and from place to place4 ,in regions of great humidity1 earth roads may be expected to have a low average of serviceability1 while in arid regions they may possess sufficient durability for a considerable volume of traffic4 ,the design adopted for earth roads and the methods of maintenance followed should therefore be carefully evolved to meet the soil and climate conditions where the roads are located4 ,these will differ greatly throughout a state or even a county4 ,cross ,sections4--,the general principles of road design were set forth in ,chapter ,,iv4 ,in ,fig4 #aa are shown typical cross sections for earth roads adapted to various conditions as indicated4 ,it is not apparent that one form of ditch is particularly preferable to the other and since some engineers prefer the ,v section and others the trapezoidal section both are shown4 ,it would appear that the ,v shaped ditch is somewhat the easier to construct with the blade grader while the trapezoidal is readily excavated with the slip or fresno scraper4 ,the ditch capacity required and consequently the dimensions will depend upon the drainage requirements1 as was pointed out in ,chapter ,,iii4 ,illustration3 ,fig4 #aa4 ,cross ,section for ,earth ,roads ,,earth ,,roads ,,in ,,regions ,,of ,,considerable ,,rainfall ,in the zones where the annual precipitation exceeds #cj inches distributed over several months1 earth roads will be unserviceable for a considerable period each year unless they are constructed so as to minimize the effect of water4 ,this is done by providing for the best possible drainage and by adopting a method of maintenance that will restore the surface to a smooth condition as quickly as possible after a period of rainy weather or after the frost comes out in the spring4 ,before the construction of the desired cross section is undertaken1 all of the grade reduction should be completed1 except for minor cuts which can be handled with the elevating grader in the manner that will be described presently4 ,where any considerable change in grade is to be effected1 the earth can be moved in several ways and of these the most economical cannot be readily determined4 ,ordinarily a contractor or a county will use the equipment that happens to be at hand even though some other might be more advantageous4 ,elevating ,grader4--,where the topography is such as to permit its use1 the elevating grader is employed in grade reduction to load the earth into dump wagons in which it is hauled to the fill or waste bank4 ,the elevating grader consists essentially of a heavy shear plow or disc plow which loosens the earth and deposits it on a moving canvas apron4 ,the apron carries the material up an incline and deposits it into a wagon which is driven along under the end of the apron4 ,when the wagon is loaded1 the grader is stopped while the loaded wagon is hauled out and an empty one drawn into position4 ,the motive power for the elevating grader is either a tractor or five or six teams of mules4 ,for many kinds of work1 particularly where frequent turning is necessary or where the ground is yielding1 mules are preferable to a tractor4 ,the apron is operated by gearing from the rear wheels of the grader4 ,generally four mules are hitched to a pusher in the rear of the grader and six or eight in the lead4 ,this method of grade reduction is particularly advantageous when the material must be hauled a distance of #ejj yards or more1 because wagon hauling in such cases is the most economical method to employ4 ,a tractor may be used to draw the elevating grader and one having a commercial rating of #cj to #de horsepower is required4 ,maney ,grader4--,if the haul is long and the nature of the cut will not permit the use of the elevating grader because of excessive grades or lack of room for turning1 a grader of the ,maney type may be used4 ,this consists of a scoop of about one cubic yard capacity1 suspended from a four-wheel wagon gear4 ,when loading1 the scoop is let down and filled in the same manner as a two-wheeled scraper or wheeler4 ,the pull required to fill a ,maney grader is so great that a tractor is ordinarily employed in place of a snap team4 ,the tractor is hitched at the end of the tongue1 without interfering with the team drawing the grader4 ,one team readily handles the grader after it is loaded4 ,for this service a tractor having a commercial rationing of #be to #cj horsepower is required4 ,wheel ,scraper4--,for moving earth for distances between #aej and #ejj yards1 the wheel scraper of a capacity of about #a-a_/b yards is quite generally employed4 ,the soil must be loosened with a plow before it can conveniently be loaded into the wheeler and a heavy plow is ordinarily employed for that purpose4 ,two furrows with the plow will loosen a strip of earth about as wide as the scoop of the scraper and if more is loosened it will be packed down by the scrapers wheeling in place to load4 ,a helper or snap team is employed to assist in loading1 after which the wheel scraper is handled by one team4 ,slip ,scraper4--,the slip scraper differs from the wheel scraper in that the scoop is not suspended from wheels but is dragged along the ground4 ,it is drawn by one team and the capacity is two to five cubic feet1 but the material spills out to some extent as the scraper is dragged along and the method is not suitable for long hauls1 #ajj feet being about the economical limit4 ,fresno ,scraper4--,the ,fresno scraper is one form of slip scraper requiring four horses or mules for efficient work4 ,it differs somewhat from the ordinary slip scraper in shape and is of larger capacity1 but is a drag type of scraper much favored in the western states4 ,,shaping ,,to ,,proper ,,cross ,,section ,if a road has been graded so that the profile is satisfactory or if the existing profile of the location is satisfactory1 and the surface is to be shaped to a prescribed cross section1 either the elevating grader or the blade grader may be employed4 ,elevating ,grader ,work4--,if the elevating grader is used in shaping the earth road1 the apron will be lowered and the material will be excavated at the sides of the road and deposited on the middle portion4 ,if slight changes in grade are desired1 wagons will accompany the grader and catch under the apron at the high places and haul the material to the low places4 ,after the earth has been deposited it must be worked over to secure the correct cross section and be made passable for vehicles4 ,this requires that clods be broken1 weeds and grass that are mixed with the earth be removed by harrowing and forking and that the surface be carefully smoothed with a blade grader4 ,this latter operation will have to be repeated several times before a satisfactory surface is secured4 ,but this miscellaneous work is highly important and under no circumstances ought to be neglected4 ,nothing so detracts from an otherwise creditable piece of work as failure to provide a smooth surface for the use of vehicles4 ,it is especially uncomfortable for the users of a highway if sods and weeds in quantity are left in the road after it has been graded4 ,the humus that will be left in the soil as the vegetable matter decays increases the porosity of the road surface making it more absorbent than soil without humus4 ,this increases the susceptibility to softening from storm water or ground water4 ,the tractor can advantageously be used to draw the elevating grader on this class of work1 but will be greatly handicapped if there are wet sections along the road1 through which the tractor must be driven4 ,in many cases its use is prohibited by such conditions and for all-round service of this character1 mules are preferred for motive power4 ,illustration3 ,fig4 #ab4--,tractor-grader ,outfit ,use of ,blade ,grader4--,heavy blade graders designed to be drawn by a tractor are suitable for shaping the earth road4 ,some of these have blades #ab feet long and excellent control for regulating the depth of cutting4 ,often two such graders are operated tandem4 ,these machines have a device which permits the operator to steer the grader independently of the tractor4 ,thus the grader can be steered off to the side to cut out the ditches1 while the tractor continues to travel on the firm part of the road4 ,earth moved with the blade grader is usually fairly free from large lumps and can readily be smoothed to a satisfactory surface for the use of traffic4 ,the sods and weeds will be drawn into the road along with the earth just as they are when the elevating grader is employed4 ,precaution must therefore be taken to eliminate them before the vegetable matter decays1 and to smooth the surface for the use of traffic4 ,costs4--,the cost of shaping an earth road in the manner described above will vary through rather wide limits because the nature and amount of work to be done varies so greatly4 ,some roads can be graded satisfactorily for #cjj4jj per mile1 while others will cost #gjj4jj4 ,but #dbe4jj per mile may be taken as an average for blade or elevating grader work plus a moderate amount of grade reduction in the way of removing slight knolls4 ,for the amount of grade reduction necessary in rolling country1 followed by grader shaping1 #ajjj4jj to #ahjj4jj per mile will be required4 ,the method is not adapted to rolling country where the roads are undulating and require some grade reduction on every hill4 ,for hilly roads one of the methods described for grade reduction will be required and the cost will obviously depend upon the amount of earth moved4 ,averages of cost figures mean nothing in such cases as the cost may reach #aj1jjj4jj per mile1 or may be as low as #bjjj4jj per mile4 ,maintenance4--,regardless of the care with which an earth road has been graded1 it will be yielding and will readily absorb water for a long time after the completion of the work4 ,the condition of the surface will naturally deteriorate rapidly during the first season it is used unless the road receives the constant maintenance that is a prerequisite to satisfactory serviceability4 ,the road drag is generally recommended for this purpose1 and if a drag is properly used it will serve to restore the shape of the surface as fast as it is destroyed by traffic4 ,good results with the drag depend upon choosing the proper time to drag and upon doing the work in the right way when using the drag4 ,the best time to drag is as soon after a rain as the road has dried out enough to pack under traffic4 ,if the work is done while the road is too wet1 the first vehicles traveling the road after it has been dragged will make ruts and to a considerable extent offset the good done by the drag4 ,if the road is too dry1 the drag will not smooth the irregularities4 ,a little observation will be required to determine the proper time for dragging on any particular soil1 but usually after a rain or thaw there is a period lasting a day or two when conditions are about right4 ,illustration3 ,fig4 #ac4--,road ,drag ,the drag is used merely to restore the shape of the surface and to do so a small amount of material is drawn toward the middle of the road4 ,but there must not be a ridge of loose material left in the middle after the work is completed4 ,some patrolmen start at one side of the road and gradually work across the road on successive trips1 finally finishing up at the side opposite that at which the start was made4 ,the next dragging should start on the opposite side from the first if that method is followed4 ,by shifting his weight on the drag1 the operator can adjust the cutting edge so that very little loose material is moved crosswise of the road and that is the proper method to pursue4 ,in that case no ridge will remain at the middle of the road4 ,if a slight one is left it should be removed by a final trip with the drag4 ,in addition to the dragging1 weeds must be cut along the road about twice a year1 the ditches must be kept cleaned out and culverts open4 ,all of the maintenance for #aj miles of earth road can be accomplished by one man giving his entire time to the work1 and that is the only method that has proven adequate to the problem4 ,,earth ,,roads ,,in ,,arid ,,regions ,in areas where the rainfall is less than #ah inches per year1 and especially where it is #aj inches or less1 an entirely different road problem exists4 ,the effect of precipitation is of significance primarily from the standpoint of erosion1 and the design of cross section and ditches and the culvert provisions are entirely different from those necessary in humid regions4 ,frequently the rainfall in semi-arid regions will be seasonal and provision must be made to care for a large volume of water during the rainy season1 but1 in general1 road design is adapted to prevention of erosion rather than to elimination of ground water effects1 or the softening effects of surface water4 ,generally the rainy period does not last long enough to warrant expensive construction to eliminate its general effects4 ,in fact1 the saturation of the soil is more likely to be a benefit than otherwise4 ,earth roads are likely to be satisfactory except where the traffic is sufficient to grind the surface into dust to such an extent that an excessive dust layer is produced4 ,in such locations the problem is one of providing a durable surface unaffected by long continued dry weather4 ,grade reduction will have the same importance as in humid areas and will be carried out in the same way4 ,maintenance will consist in repairing the damage from occasional floods and in removing or preventing accumulations of drifting sand or dust4 ,crude petroleum oils have been satisfactory for maintenance in such locations when used on stable soils4 ,value of ,earth ,roads4--,the serviceability of the earth road depends to a large extent upon the care exercised in its maintenance4 ,the only part of earth road construction that is permanent is the grade reduction4 ,the cross section that is so carefully shaped at considerable cost may flatten out in one or two years1 especially if the road goes through unusually wet periods4 ,traffic will continually seek a new track during the period when the road is muddy and is as likely to cross the ditch to the sod near the fence as to use any other part of the road4 ,continual and persistent maintenance is therefore essential to even reasonable serviceability4 ,at best the earth road will be a poor facility for a considerable period each year in the regions of year-around rainfall4 ,in most localities1 roads of distinctly minor importance are of necessity only earth roads and for the comparatively small territory they serve and the small amount of traffic1 they probably serve the purpose4 ,for roads of any importance in the humid areas of the ,united ,states1 the earth road cannot carry satisfactorily the traffic of a prosperous and busy community4 ,,chapter ,,vi ,,sand-,,clay ,,and ,,gravel ,,roads ,in ,chapter ,,iv1 mention was made of the variation in serviceability of road surfaces composed of the natural soil existing on the right-of-way of the road4 ,it has been found that soils of a clayey nature in which there is a considerable percentage of sand usually afford a serviceable road surface for light or moderate traffic1 especially in areas where climatic conditions are favorable4 ,a study of these soils1 together with the construction of experimental roads of various mixtures of sand and clay1 has led to a fairly comprehensive understanding of the principles of construction and range of capacity of this type of road surface1 which is known as the sand-clay road4 ,the sand-clay road surface consists of a natural or artificial mixture of sand and clay1 in which the amount of clay is somewhat greater than sufficient to fill the voids in the dry sand4 ,it may be assumed that the sand contains #dj per cent of voids and that at least #de per cent of clay is required to fill the voids and bind the sand grains together1 because the clay spreads the sand grains apart during the mixing1 thus having the effect of increasing the voids4 ,as a matter of experiment1 it is found to be impractical to secure by available construction methods mixtures of sufficient uniformity to render it necessary to exercise great exactness in proportioning the components1 but reasonable care in proportioning the materials is desirable4 ,successful utilization of this type of surface requires considerable study of available materials and investigations of their behavior when combined4 ,extensive and exhaustive experiments have been conducted with sand-clay mixtures in various places where they are widely used for road surfaces and the following general principles have been deduced4 ,the ,binder4--,in the sand-clay road1 stability is obtained by utilizing the bonding properties possessed to some degree by all soils4 ,naturally this characteristic may be expected to vary widely with the several types of soil4 ,it is generally considered to be a common property of clay1 but the term clay is a general one that is often applied to soils differing greatly in physical characteristics and the term therefore loses its significance in this connection4 ,those soils that are properly and technically called clay are decidedly sticky when wet and are the best materials for sand-clay construction4 ,of the clays1 those that produce a tough sticky mud are best4 ,this can be tested by mixing a small quantity into a stiff mud and molding it into a ball and immersing in water4 ,if the ball retains its shape for some little time1 it is likely to prove a very satisfactory binder1 but1 if it becomes plastic and loses its shape1 it will be an inferior binder1 as a general rule4 ,the ball clay1 as the former is called1 may be of any color common to soils1 not necessarily yellow or reddish as is sometimes supposed4 ,likewise1 balls of mixtures containing varying percentages of sand and the binder to be used may be made up and immersed in water4 ,the mixture that holds its shape longest is of course the best combination of the materials and indicates the mixture to use in the construction4 ,an ideal1 or even a fairly satisfactory soil for a binder may not exist in the vicinity of a proposed improvement1 and consequently an inferior binder is frequently the only material available4 ,sometimes deposits of clay or gravel contain a considerable percentage of gypsum which serves as a binder and is particularly effective when used in combination with clay and sand or gravel4 ,in many places a soil of the type used for adobe and called caliche may be found and this is an excellent binder for sand or gravel4 ,top-,soil or ,natural ,mixtures4--,deposits consisting of a natural mixture of sand and clay in which the ingredients happen to exist in about the correct relative proportions for sand-clay road surfaces are found in many localities4 ,these mixtures are commonly referred to as top-soil4 ,if the deposits are somewhat deficient either in sand or clay1 they can be utilized if the proper corrections in the proportions are made during construction4 ,very satisfactory road surfaces are sometimes constructed with mixtures that appear to be far from ideal in composition1 but experience and frequent trials are needed to determine the best way in which to handle these mixtures4 ,sand-,clay ,surfaces on ,sandy ,roads4--,sand-clay surfaces may be constructed on naturally sandy roads either by adding clay and mixing it with the sand to secure the desired composition1 or a layer of a natural sand-clay mixture1 caliche or sand-clay-gypsum may be placed on top of the sand4 ,the most widely used method is to mix clay or other binder with the sand4 ,since there is no need to provide for ditches to carry storm water on a deep sand soil1 the sand is graded off nearly flat across the road and no ditches are provided4 ,the clay is dumped on the road in a layer about #h inches thick and is then mixed into the sand4 ,it is desired to mix enough sand with the clay to produce a mixture composed of approximately #a_/c clay and #b_/c sand4 ,the mixing is accomplished in various ways1 the most common being to use a heavy plow at first and to follow this with a heavy disc harrow4 ,the mixing is a tedious and disagreeable process1 but its thorough accomplishment is indispensable4 ,the mixing is most readily done when the materials are saturated with water and in practice it is customary to depend upon rain for the water1 although in the final stages water may be hauled and sprinkled on the road to facilitate final completion of the mixing4 ,after the mixing has been completed1 the surface is smoothed with the blade grader and is kept smooth until it dries out4 ,repeated dragging will be required1 during the first year especially1 and to some extent each year in order to keep the surface smooth1 but the dragging can be successfully accomplished only when the road is wet4 ,illustration3 ,fig4 #ad4--;,cross ,sections for ,sand-,clay ,roads ,in regions where several months of continued hot1 dry weather is to be expected each year1 the sand-clay mixture is likely to break through unless it is of considerable thickness and generally the surface layer is made much thicker than for regions where the annual rainfall is fairly well distributed4 ,this is especially necessary when the binder is of inferior quality4 ,it is not uncommon in such cases to make the sand-clay surface as much as two feet thick4 ,as the mixing progresses it may appear that patches here and there are deficient in either clay or sand and the mixture in these places is corrected by the addition of a little sand or clay as may be required4 ,if the top-soil is used it is deposited on the sand in the required quantity and is remixed in place to insure uniformity4 ,if either sand or clay is needed to give a satisfactory mixture1 the proper material is added and mixed in as the work progresses4 ,the surface is finally smoothed by means of the grader and drag4 ,sand-,clay on ,clay or ,loam4--,if the existing road is of clay or loam1 ample drainage will be required as discussed in ,chapter ,,iv4 ,the surface may be constructed of a natural sand-clay mixture or of a sand mixed with the natural soil4 ,if the former1 the surface of the existing road is prepared by grading so as to insure good drainage and the natural mixture is then deposited and the surface completed as described in the preceding section4 ,if the surface is formed by mixing sand with the existing soil1 the sands may be deposited in a layer about six inches thick which will gradually mix with the soil as the road is used4 ,a second application of sand may follow in a year or two if it is needed4 ,such a road surface will lack uniformity of composition and it seems preferable to mix the sand with the soil by plowing and discing as previously described4 ,characteristics4--,sand-clay road surfaces do not have sufficient durability for heavily traveled highways1 but will be satisfactory for a moderate amount of traffic4 ,these surfaces have maximum serviceability when moist1 not wet1 and consequently are not as durable in dry climates as in humid areas4 ,they are likely to become sticky and unstable in continued wet weather and to become friable and wear into chuck holes in long continued dry weather4 ,at their best1 they are dustless1 somewhat resilient and of low tractive resistance4 ,,gravel ,,road ,,surfaces ,illustration3 ,fig4 #ae4--;,cross ,sections for ,gravel ,highways ,natural ,gravel4--,gravel is the name given to a material consisting of a mixture of more or less rounded stones1 sand and earthy material1 which is found in natural deposits4 ,these deposits exist in almost every part of ,north ,america1 being especially numerous in the glaciated areas1 but by no means confined to them4 ,gravel deposits consist of pieces of rock varying in size from those of a cubic yard or more in volume to the finest stone dust1 but with pieces ranging in size from that which will pass a #c-;inch ring down to fine sand predominating4 ,the larger pieces are usually more or less rounded and the finer particles may be rounded or may be angular4 ,many varieties of rocks are to be found among the gravel pebbles1 but the rocks of igneous origin and possessing a considerable degree of hardness generally predominate4 ,intermixed with the pieces of rock there is likely to be clay or other soil1 the quantity varying greatly in different deposits and even in various places in the same deposits4 ,often there are found deposits of material which are by the layman termed gravel1 which are really clayey sand or sand containing a few pebbles1 but which are of value to the road builder for the sand clay type of surfacing4 ,the term gravel is exceedingly general and unless specifically defined1 gives little indication of the exact nature of to which it is applied4 ,,table #g ,,showing ,,cementing ,,properties ,,of ,,several ,,samples ,,of ,,gravel ---------------------------------------- ----- ,cementing ,value ,per ,cent ,clay by --------------------------- ,weight ,as ,received ,washed ---------------------------------------- ---- #d4d #bgf #dc #f4d #aje #bhe #e4a #bda #gj #ad4e #ejj #bgi #h4e #ejj #aab #aj4a #cjj #bfg #ad4h #ejj #ajg #g4e #ahd #aih #af4e #ejj #dbh #b4j #ahe #bci #a4e #ejj #ejj #d4e #bab #bjd #b4e #aaf #cfc ---------------------------------------- ---- ,the value of any gravel for road surfacing depends upon the degree to which it possesses the properties of an ideal gravel for road surfacing4 ,ideal gravel is seldom encountered1 but a consideration of its characteristics serves to establish a measure by which to estimate the probable value of any deposit4 ,the ,ideal ,road ,gravel4--,the ideal road gravel is a mixture of pebbles1 sand and earthy material1 the pieces varying from coarse to fine in such a manner that when the gravel is compacted into a road surface the spaces between the larger pebbles are filled with the finer material4 ,the pebbles are of a variety of rock that is highly resistant to wear so that the road surface made from the gravel will have the quality of durability4 ,the gravel possesses good cementing properties1 insuring that the pieces will hold together in the road surface4 ,the cementing property may be due to the rock powder in the deposit or to earthy material mixed with the rock particles1 or to both4 ,table #g shows the results of a number of tests made upon gravels and indicates that the cementing property of the gravel does not always depend upon the clay content4 ,permissible ,size of ,pebbles4--,the larger pebbles in the gravel are less likely to crush under loads than smaller pebbles of the same sort of rock1 but if the rock is of some of the tougher varieties such as trap1 there is very little likelihood of even the smaller pebbles crushing4 ,if the pebbles are of rock of medium toughness1 the smaller pebbles might be crushed under the heavier loads4 ,it is the usual practice to permit gravel to be used for the foundation course in which the pebbles are as large as will pass a #c-a_/b-;inch circular screen opening1 and for the wearing course1 as large as will pass a #b-a_/b-;inch circular screen opening4 ,if larger pebbles are allowed in the wearing course1 the surface is certain to become rough after a time4 ,if the gravel is to be placed in a single course as is a very common practice1 then the maximum size should not exceed that which will pass a #b-a_/b-;inch circular screen opening4 ,the ,wisconsin ,highway ,commission has constructed a very large mileage of excellent gravel roads and the sizes specified for their roads are as follows3 ,bottom ,course ,gravel4--,bottom course shall consist of a mixture of gravel1 sand and clay with the proportions and various sizes as follows3 ,all to pass a two-inch screen and to have at least sixty and not more than seventy-five per cent retained on a quarter-inch screen2 at least twenty-five and not more than seventy-five per cent of the total coarse aggregate to be retained on a one-inch screen2 at least sixty-five and not more than eighty-five per cent of the total fine aggregate to be retained on a two hundred-mesh sieve4 ,top ,course ,gravel4--,top course shall consist of a mixture of gravel1 sand and clay with the proportions of the various sizes as follows3 ,all to pass a one-inch screen and to have at least fifty and not more than seventy-five per cent retained on a quarter-inch screen2 at least twenty-five and not more than seventy-five per cent of the total coarse aggregate 7material over one-fourth inch in size7 to be retained on a one-half-inch screen2 at least sixty-five and not more than eighty-five per cent of the total fine aggregate 7material under one-fourth inch in size7 to be retained on a two hundred-mesh sieve4 ,screened ,gravel and ,sand ,mixtures4--,where it is impossible to obtain run of bank gravel containing the necessary binder in its natural state1 screened gravel shall be used and the necessary sand and clay binder added as directed by the engineer4 ,gravel and sand shall be delivered on the work separately4 ,clay binder shall be obtained from approved pits and added as directed by the engineer4 ,run of ,bank ,gravel4--,when run of bank gravel is permitted either for one course or two course work1 the size shall not exceed that specified for bottom or top course4 ,if necessary1 the contractor shall pass all the material through a two-inch screen for the bottom course1 and through a one-inch screen for the top course4 ,when the work consists of only one course1 the material shall be of the sizes as specified for the top course4 ,the necessary binder shall be contained in the material in its natural state1 excepting that a small percentage of clay binder may be added as directed by the ,engineer4 ,wearing ,properties4--,a certain amount of grinding action takes place on the road surface under the direct action of wheels1 especially those with steel tires4 ,where rubber tired traffic predominates1 this action is much less severe than where steel tired vehicles predominate1 but the tendency exists on all roads4 ,in addition1 there is distortion of the layer of gravel under heavy loads which causes the pieces of stone in the surface to rub against each other and to wear away slowly4 ,the gravel road in the very best condition is slightly uneven but there is comparatively little jar imparted to vehicles1 and1 consequently1 little impact on the surface4 ,when somewhat worn1 the impact becomes a factor of some importance and the pounding of vehicles has a very destructive action on the surface4 ,soft pebbles will be reduced to dust in a comparatively short time4 ,the degree to which any gravel resists the destructive action of traffic depends upon the varieties of rock represented by the pebbles in the gravel4 ,if the pebbles are mostly from rocks of good wearing properties1 that quality will be imparted to the road surface4 ,if mostly from rocks of little durability1 the same characteristic will be imparted to the road surface4 ,a very good general notion of the probable durability of gravel can therefore be obtained by a careful visual examination of the material and classification of the rock varieties represented by the pebbles4 ,utilizing ,natural ,gravels4--,gravel road construction is advantageous only when it can be accomplished at low first cost4 ,this usually presupposes a local supply of gravel that can be utilized1 or at any rate a supply that need not be shipped a long distance4 ,in the nature of things1 such deposits are likely to be deficient in some of the desirable characteristics1 and may be deficient in most of them4 ,by various means1 the defects in the materials can be partially corrected while constructing the road4 ,if the gravel deposit consists of layers of varying composition as regards size and clay content1 the material may be loosened from the exposed face and allowed to fall to the bottom of the pit thereby becoming mixed to a sufficient extent to produce a reasonably uniform product4 ,if deficient in clay1 it often proves feasible to add a small part of the clay over-burden1 thereby insuring enough binder4 ,sometimes adjoining deposits will consist one of relatively fine material1 the other of relatively coarse4 ,these may be mixed on the work by first placing the coarse material in a layer about #e inches thick and adding the finer material in a similar layer4 ,the two will mix very rapidly during the operations of spreading and shaping4 ,when deposits contain pebbles larger than will pass a #c-a_/b-;inch ring1 these larger stones will prove to be undesirable if placed on the road1 as they are almost sure to work to the surface of the gravel layer and become a source of annoyance to the users of the road4 ,oversize stone can be removed while loading the gravel or while spreading it1 if care is exercised and not too large a proportion is oversize4 ,it is preferable however to remove the oversize by means of screens at the pit4 ,usually on large jobs the oversize is crushed and mixed with the supply so as to utilize what is really the best part of the material4 ,gravels deficient in bonding material are often encountered in deposits where there is insufficient overburden to give enough additional binder or where the overburden is of a material unsuitable for binder4 ,such materials may be utilized by adding binder in the form of clay after the gravel has been placed on the road4 ,almost any gravel deposit can be utilized in some way if the material is of a durable nature1 regardless of other characteristics4 ,the serviceability of a gravel road will depend largely on how nearly the gravel approaches the ideal1 but variations in the manipulations will do much to overcome deficiencies in materials4 ,thickness of ,layer4--,the thickness of the layer of gravel required depends both upon the type of soil upon which it is placed and the nature of the traffic to which the road will be subjected4 ,gravel surfaces should not ordinarily be constructed on highways carrying heavy truck traffic1 but if gross loads of three or four tons are the heaviest anticipated1 the gravel will be reasonably stable4 ,on such roads1 a layer of well compacted gravel ten inches thick will support the loads if a well drained earth foundation is provided4 ,if but little truck traffic is anticipated and loads up to three tons on steel tires are the average1 a layer #h inches thick will be sufficient4 ,in dry climates1 a layer six inches thick will be adequate if it can be kept from raveling4 ,on secondary roads1 carrying principally farm-to-market traffic1 and not a great volume of that1 the above thicknesses may be reduced about one-fourth4 ,the exact thickness needed for any particular road is a matter for special study on account of the variations in the gravels and in the supporting power of the soil upon which they are placed4 ,,placing ,,gravel ,preparation of the ,road4--,the roadway that is to be surfaced with gravel is first brought to the desired grade and cross section4 ,it would be advantageous if this could be done a year before the gravel is placed so that no settlement of the earth foundation would occur after the gravel surface is completed4 ,but if that is impractical1 the grading may be done just prior to placing the gravel1 providing appropriate methods are adopted for securing compacted fills4 ,trench ,method4--,two distinct methods of placing the gravel are in general use1 known as the trench method and the surface or feather edge method respectively4 ,the method to adopt for any particular road will depend largely on certain conditions that will be explained later4 ,in the trench method1 a trench of the proper width and depth for receiving the gravel is excavated in the earth road surface and the gravel is placed therein4 ,the trench is formed by plowing a few furrows and scraping out the loosened earth with a blade grader4 ,the loose material is generally moved out laterally to build up earth berms or shoulders alongside the gravel4 ,into this trench the gravel is dumped in the proper quantity to give the required thickness after being compacted4 ,the greatest care must be exercised in spreading the gravel to eliminate unevenness where the loads were deposited4 ,an ordinary blade grader is one of the best and most economical implements to use for spreading the gravel4 ,when the gravel has been deposited in the trench for a distance of a thousand feet or more1 the spreading is accomplished by dragging the surface repeatedly with the blade grader1 the work being continued until all waviness disappears4 ,the gravel is then thoroughly and repeatedly harrowed with a heavy stiff tooth harrow to mix thoroughly the fine and coarse gravel so as to produce as nearly a uniform mixture as may be4 ,the gravel is then finally smoothed with the blade grader4 ,the gravel may be compacted by rolling or may be allowed to pack from the action of traffic4 ,the former is greatly to be preferred where practicable4 ,the rolling is performed with a three-wheeled self-propelled roller weighing about #h tons and must be done while the gravel is wet4 ,generally a sprinkling wagon is used to wet down the gravel1 but advantage is always taken of rains to facilitate the work4 ,the gravel must be spread in layers not over #e or #f inches thick to get the desired results1 which means that for an ordinary gravel road about #aj inches thick1 the gravel will be placed in two layers of about equal thickness1 each of which will be rolled4 ,the gravel will compact slowly even if it is not rolled1 but generally does not become stable until the material is thoroughly soaked by rains4 ,then it will begin to pack1 but will become badly rutted and uneven during the process4 ,during this period the surface must be kept smooth by means of the blade grader4 ,the drag does not suffice for this purpose1 tending to accentuate the unevenness rather than to correct it4 ,if gravel is placed in a trench in dense soil and rainy weather ensues1 sufficient water will be held in the trench to cause unevenness from foundation settlement and the gravel will become mixed with the soil to some extent and be thereby wasted4 ,trenches cut from the road bed upon which the gravel is placed1 to the side ditches1 will relieve this condition by affording an outlet for the surplus water4 ,nevertheless some difficulty may be expected if the trench method is used and wet weather prevails4 ,if it is possible to close the road against traffic until the road is dry the method is applicable4 ,moreover1 in long-continued dry weather1 the dispersion and loss of considerable gravel from the action of automobile traffic is avoided because the gravel is held between substantial earth berms and the gravel will pack better and hold its shape longer when constructed by the trench method than otherwise4 ,surface ,method4--,the surface method is one in which the gravel is placed on the graded earth road surface without earth shoulders to hold the gravel in place4 ,it is also sometimes called the feather-edge method4 ,except for the manner of placing as just mentioned1 the several operations are conducted in the same general manner as for the trench method4 ,the gravel does not compact as quickly as in the trench method and a considerable loss of material is likely to result from the effect of automobile traffic while the gravel is loose4 ,but it has the advantage of being free from difficulties in wet weather and in some locations is therefore preferable to the trench method4 ,it is particularly applicable to those projects on which the placing of gravel continues throughout the winter1 the gravel being dumped and spread1 to be finally smoothed and finished in the early summer4 ,bonding4--,where gravels deficient in binder are utilized1 clay for binder is sometimes added as the gravel is placed on the road4 ,this may be done by spreading the clay on top of the lower course of gravel1 placing the upper layer and sprinkling and rolling until the clay squeezes up through the surface layer4 ,it may also be accomplished by spreading dry clay on the upper course before it is harrowed and then harrowing to mix it with the gravel4 ,both methods are practiced1 but the former is believed to be preferable4 ,a third method is to separate the sand and pebbles and to mix the clay binder with the sand and then spread the sand on top of the pebbles and mix by harrowing4 ,maintenance4--,gravel surfaces require careful maintenance1 especially during the first season the road is used4 ,the gravel will compact slowly and during the process will be rutted and otherwise disturbed by traffic4 ,it is important during this period to restore the shape once a week or at least twice a month4 ,the light blade grader is usually employed for the purpose so long as the gravel is somewhat loose4 ,later a drag of the type known as the planer will prove to be the most effective4 ,figure #af shows a type of drag that is very satisfactory for use on gravel roads4 ,illustration3 ,fig4 #af4--,road ,planer ,,chapter ,,vii ,,broken ,,stone ,,road ,,surfaces ,the broken stone road surface1 or macadam road as it is usually termed1 consists of a layer of broken stone1 bonded or cemented together by means of stone dust and water4 ,the surface may or may not be coated with some bituminous material4 ,design4--,it has been an accepted assumption that the macadam road surface is somewhat more stable than the gravel road surface of equal thickness1 and since this is probably the consensus of opinion of engineers familiar with both types1 it may be accepted until experimental data are available on the subject4 ,the thickness of the layer of macadam required for a road will depend upon the same factors that were considered in connection with the thickness of the gravel surface1 i4e41 kind of stone used1 character of earth foundation and nature of the traffic4 ,the standard macadam surface where good earth foundation is to be had and where the loads do not exceed about four tons has for years been eight inches thick4 ,for heavier loads or inferior foundation1 a somewhat greater thickness would be employed1 but the best practice would probably provide a foundation course of the ,telford type for doubtful foundation conditions1 especially for the extremely uncertain cases4 ,for soils of very good supporting strength such as very sandy loam or deep sand or for arid regions where stable foundation is always assured the thickness of the macadam might be reduced to six inches4 ,it should be borne in mind that the broken stone road is not adapted to the traffic carried by trunk line highways in populous districts1 but is rather a type permissible on secondary roads and usually adequate for local roads4 ,it should never be employed for roads carrying any considerable volume of passenger automobile traffic or motor truck traffic4 ,if surfaced with a bituminous material it will carry up to #abjj passenger automobiles per day1 but not to exceed fifty trucks4 ,properties of the ,stone4--,the stone employed for the broken stone road should possess the qualities of hardness and toughness and should be capable of resisting abrasion sufficiently well to have reasonable life under the traffic to which it is subjected4 ,since the traffic may vary from very light on some roads to far beyond the limit of the economical capacity of this type of pavement on others1 it follows that any particular deposit of stone might be durable enough for some roads1 while for others it might be entirely inadequate4 ,as a general rule it has been found that stone that wears away at a moderate rate will1 when used for water-bound macadam surface1 result in a smoother trackway than one that will wear very slowly4 ,it is not therefore altogether certain that the most durable stone to be had should be selected for a particular road4 ,this is especially true now that the water-bound macadam surface has been largely superseded for trunk line highways and other heavily traveled roads1 and is employed in locations where service conditions are not severe4 ,the stone employed for the water-bound macadam surface must possess good cementing properties1 because the surface depends for stability primarily upon the bonding action of the dust from the broken stone4 ,this is in contrast to the gravel road1 where little dependence is placed upon the bonding effect of the rock dust4 ,in preparing the stone for macadam surfaces1 the ledge rock is crushed and screened1 and in that way a supply of the finer particles1 which are a part of the output of the crusher1 is obtained for use in bonding the surface4 ,this finely broken material1 usually called screenings1 is essential to the construction of the water-bound type of surface4 ,rocks vary considerably in the cementing properties of the dust1 but usually the rocks classed as trap1 such as andesite1 gabbro and rhyolite1 and schist and basalt possess good cementing properties4 ,limestones usually possess good cementing properties1 but some of the dolomitic limestones are of low cementing value4 ,quartz1 sandstone and the granites are of low cementing value4 ,kinds of ,rocks ,used for ,macadam4--,limestone and chert are the two sedimentary rocks1 employed most extensively for broken stone roads4 ,these rocks are found in widely distributed areas and vary in physical characteristics from very soft material of no use to the road builder to materials possessing considerable durability4 ,it is desirable to carefully test out the deposits of these materials before using to ascertain the probable value of the rock1 for the construction of the road surface4 ,of the igneous rocks1 those classed as trap are best known to the road builder and many of the deposits of trap rock afford an excellent material for broken stone roads where the severest conditions of traffic are encountered4 ,the trap rocks are tough and durable and generally possess excellent cementing properties4 ,granite and sandstone are seldom used for water-bound macadam as they possess poor cementing properties and a binder of some kind must be added to cement the pieces together4 ,for this purpose clay or the screenings from some other variety of stone may be utilized4 ,some other materials are occasionally employed for the construction of macadam surfaces4 ,of these1 oyster or marine shells1 burnt shale1 and slag are most common4 ,shells and slag are of rather low durability but possess good cementing properties4 ,shale is a makeshift suitable only for very light traffic roads4 ,sizes of ,stone4--,the stone for the wearing course of a macadam road should be as large as practicable1 because the larger the pieces the more durable the surface4 ,if the individual stones are too large it is difficult to secure a smooth surface1 and large stones will be readily loosened by tipping as the wheels roll over them4 ,these considerations limit the size to a maximum of that which will pass a #b-a_/b-;inch screen4 ,stone of excellent wearing qualities may be somewhat smaller1 but never less than that which will just pass a #a-a_/b-;inch screen4 ,for the lower course1 the size is not particularly important except where the earth foundation is such as to require special construction4 ,it is not uncommon to use the same size of stone for both upper and lower course and yet in many instances stone up to that which will just pass a #c-a_/b-;inch screen is used for the lower course4 ,stone much smaller in size may also be used successfully1 but if the stone is broken to a smaller size than is required1 unnecessary expense is incurred4 ,the bonding material is the finer portion of the product of the crusher1 which is called screenings4 ,this material may be so finely crushed as to pass a one-fourth inch screen1 or may be so coarse as to just pass a one-half inch screen1 but in any case must contain all of the dust and fine material produced by the crusher4 ,where the soil and drainage conditions demand an especially stable foundation course1 the ,telford type is used4 ,the ,telford foundation consists of a layer of stones of various dimensions that can be laid so as to give a thickness of #h inches4 ,these large stones are placed by hand and therefore the size requirements are not rigid4 ,stones having one dimension about #h inches and the others not over #aj or #ab inches are satisfactory4 ,earth ,work4--,a thoroughly drained and stable earth foundation is essential to success with the macadam type of surface4 ,before placing the stone1 the road must be shaped to the proper cross section and all grade reduction work completed4 ,preferably heavy fills should have a year to settle before the macadam surface is placed4 ,side ditches1 necessary culverts and tile drains should be constructed as required for drainage4 ,the earth work is often carried out in connection with the construction of the macadam surface1 being completed just ahead of the surfacing4 ,in that case1 the fills must be carefully rolled as they are placed4 ,the road bed may be shaped in connection with the other earthwork4 ,if the road has been brought to a satisfactory grade some time prior to placing the macadam1 the road bed for the broken stone will be prepared as needed for placing the stone4 ,foundation for the ,macadam4--,macadam surfaces are quite generally placed in a trench as described in the trench method for placing gravel4 ,it is an almost universal practice to compact the layer of stone by rolling with an #h- or #aj-ton power roller1 and if the stone is not held between substantial earth berms or shoulders1 the rolling merely serves to spread the stone out over the road bed instead of compacting it4 ,if an attempt is made to roll broken stone which has been placed on a yielding foundation1 no benefit results1 but on the contrary the stone is likely to be forced down into the soil4 ,to insure that the layer of broken stone can be compacted by rolling1 it is first necessary to roll the earth foundation until it becomes hard and unyielding4 ,if soft or yielding places appear during the rolling these should be corrected by tile drains or by removing the earth from the spongy place and back-filling with material that will compact when rolled4 ,it is not always easy to determine why these soft places exist in what appears to be a well drained roadway1 especially since they are as likely to be found on fills as anywhere else4 ,apparently they are due to local pockets of porous soil held by denser soil so that the water does not readily drain away4 ,it is usually true that such places are observed during the season of frequent precipitation more often than during other seasons of the year4 ,in dry climates1 the difficulties of securing suitable foundations for the broken stone road are largely eliminated1 but it may be observed that this type of surface is not suitable for such climates unless some sort of bituminous binder is employed to hold the stones in place4 ,the cementing power of the stone dust is inadequate when the surface is continually dry4 ,illustration3 ,fig4 #ag4--;,cross ,section for ,macadam ,telford ,foundation4--,when the ,telford type of foundation is employed1 the earth subgrade is prepared and then the ,telford stone placed carefully by hand4 ,the spaces between the large stones are filled with the spalls broken from the larger stones in fitting them in place4 ,when completed the base is rolled with a heavy roller to secure a firm unyielding layer4 ,the thickness is generally about eight inches4 ,any fairly sound stone may be used for the ,telford base4 ,placing the ,broken ,stone4--,it has been found impracticable properly to roll a greater thickness than about #e or #f inches of loose stone1 therefore1 the stone for the macadam surface is usually placed in two layers1 the first or lower layer being rolled before the next layer is placed4 ,the stone is hauled in dump wagons1 trucks or dump cars1 dumped on the road bed and spread by hand rakes or by means of a blade grader and is then rolled4 ,to insure the proper thickness the loads are accurately spaced to spread to the proper thickness4 ,rolling4--,a three-wheeled or macadam type of roller1 of the self-propelled type1 is best for compacting the broken stone road4 ,the weight varies from eight to fifteen tons1 but for most conditions the ten or twelve ton size seems to be preferable4 ,on ,telford base construction1 a heavier machine is desirable and for very hard stone it may be successfully employed4 ,the first trip with the roller is made along the edge of the stone and each successive trip is made a little nearer the middle until finally one half of the strip of stone has been rolled4 ,the roller is then taken to the opposite side of the roadway and the operation repeated on the other half4 ,the rolling is continued until the stone is thoroughly compacted1 which is evidenced by the fact that the roller makes but a slight track in the surface4 ,the second layer of stone is then placed and rolled in the same manner as the first4 ,spreading ,screenings4--,after the upper course has been rolled1 the screenings are spread on it from piles alongside the road1 enough being used to fill the voids in the layer of stone and furnish a slight excess4 ,as the screenings are spread they are rolled to work them into the voids4 ,when these are filled1 the surface is sprinkled thoroughly by means of an ordinary street sprinkling cart and again rolled4 ,in this way the dust and water are mixed into a mortar which fills the crevices between the stones4 ,this mortar hardens in a few days1 giving a bond that is weak1 but sufficient for the purpose if the traffic is not too heavy4 ,a broken stone road finished in this way is called a water-bound macadam1 and is ready for traffic in three or four days after completion4 ,bituminous ,surfaces4--,on account of the inadequacy of the water-bound macadam when subjected to motor traffic and to obviate the tendency of broken stone surfaces to loosen in dry weather1 there has been developed a method of covering the surface with a bituminous material such as tar or asphalt4 ,this will be described in detail in a later chapter4 ,maintenance4--,even under favorable conditions as regards kind and amount of traffic the macadam road requires constant maintenance4 ,the first effect of traffic will be to brush away the fine materials used for bonding the surface1 thus exposing the larger stones in such a way that they are rather easily loosened and removed from the surface by wheels and the hoofs of animals4 ,this finer material must be replaced as fast as it is removed so as to protect the surface4 ,either stone dust or clayey sand may be used1 but clay if used alone is likely to be sticky when wet and prove to be worse than the condition it was expected to correct4 ,in time1 ruts and depressions will appear1 either as the gradual effect of wear1 which will inevitably effect some portions of the surface more than others1 or on account of subsidence of the foundation4 ,uneven places are repaired by first loosening the stone1 then restoring the cross section by adding new material and tamping or rolling it in place4 ,if a bituminous coating has been applied1 it will eventually peel off in places and these places must be recoated as soon as practicable4 ,eventually the surface will be worn to such an extent that an entirely new wearing surface must be added4 ,this is done by loosening the entire surface to a depth of #c or #d inches and then adding a new layer of broken stone4 ,the loosening is sometimes accomplished by means of heavy spikes inserted in the roller wheels1 and at others by means of a special tool known as a scarifier4 ,the new surface is placed and rolled in precisely the same manner as the wearing surface of the original construction1 but the layer may not be as thick as the original wearing course4 ,a new course will not bond to the old surface unless the old macadam has been thoroughly broken up first4 ,characteristics4--,the water-bound macadam is a dusty1 somewhat rough surface of low durability for rubber tired vehicles4 ,it has long been the standard rural highway for steel tired vehicles1 but cannot carry any considerable amount of motor traffic4 ,it is easily repaired4 ,when finished with a bituminous surface its durability is greatly increased and the dust is eliminated4 ,it does not seem to be sufficiently rigid for truck traffic1 unless placed on exceptionally good foundation4 ,,chapter ,,viii ,,cement ,,concrete ,,roads ,the cement concrete road is one of the later developments in highway construction1 but the type has had sufficient use to show that it is one of the satisfactory types for heavy mixed traffic1 and1 where the proper materials are available1 it is one of the economical types of construction4 ,destructive ,agencies4--,it is well to have clearly in mind at the outset that the concrete in a road surface is subjected to certain destructive agencies not usually significant in connection with the use of concrete1 and these are so often disregarded that the average serviceability of the concrete road surface is sometimes much lower than it would be if built with due regard for the effect of traffic on concrete surfaces4 ,in most structural uses of concrete1 its strength in compression only is utilized1 and the factor of safety is such as to eliminate to some extent failures due to inferior materials or workmanship4 ,the concrete road surface is subjected to compression under wheel loads1 to bending1 causing tension in the concrete1 to abrasion from wheels1 and to tension and compression due to effect of temperature4 ,the weight of the wheel loads may cause sufficient distortion of the road slab to produce rupture4 ,the aggregates may be crushed under wheel loads if the material is too soft4 ,abrasion from steel tired vehicles wears away the concrete unless it is hard and durable4 ,changes in dimension due to the effect of change in temperature introduce tension or compression into the road slab and may result in cracks4 ,freezing and thawing in the subgrade subjects the slab to vertical movement and discontinuous support with the result that longitudinal and transverse cracks occur4 ,the foregoing indicates the importance of securing good concrete for road surfacing1 and that is accomplished by using suitable aggregates1 by proper design of the road surface and by following established construction methods4 ,design4--,the widths usually adopted for concrete roads are3 for single track roads1 #i or #aj feet1 and for double track roads1 #ah or #bj feet4 ,the thickness is #f to #h inches at the middle1 varying with climatic conditions and with the kind of soil upon which the concrete is laid4 ,the thickness at the edge is #a inch less than at the middle except that #f-;inch surfaces are usually of uniform thickness1 the total crown being #b inches4 ,the thickness of the two course pavement is the same as would be used for a single course pavement in the same location4 ,the surface of either width has a total crown of one or two inches to insure water running off the surface4 ,the earth foundation is often flat1 the crown being obtained by making the slab thicker at the middle than at the edge4 ,fig4 #ah shows cross section for concrete roads4 ,illustration3 ,fig4 #ah4--;,cross ,section for ,concrete ,highway ,in the state of ,california1 concrete roads four or five inches thick and surfaced with a bituminous carpet mat have been successfully constructed4 ,similar designs have been used in a few other places1 but for general practice it is unsafe to depend upon such a thin slab4 ,climatic and soil conditions probably account for the success of the thin roads in ,california4 ,concrete ,materials4--,the coarse aggregate for the concrete may be broken stone or pebbles screened from natural gravel4 ,durability is necessary1 but it is also important to have uniformity in the concrete so that the road surface will wear uniformly and consequently keep smooth4 ,supplies of broken stone are likely to contain a small percentage of soft pieces and such of these as are at the surface when the concrete is finished will crush under traffic1 leaving a pit in the surface4 ,pebbles screened from gravel are also likely to be variable in durability and should be carefully inspected if they are to be used as aggregate for concrete roads4 ,the harder limestones1 some sandstones1 pebbles from many of the gravel deposits and practically all of the igneous rocks make satisfactory aggregates for the concrete road4 ,sometimes none of the coarse aggregates readily available are sufficiently durable or uniform for the wearing surface of the concrete road1 but a suitable aggregate may be obtained at relatively high price by shipping considerable distances4 ,in such cases what is known as the two course type of concrete road is employed4 ,the wearing course usually is about #b inches thick and is constructed with selected aggregates of good quality shipped in for the purpose4 ,the lower course is constructed of aggregates which do not possess the desired qualities for a wearing course1 but which are satisfactory for concrete not subjected to abrasion4 ,the aggregates for the wearing course will be selected with the same regard for uniformity and durability that would be the case if they were for the one course pavement4 ,bank run gravel1 or run of the crusher stone1 is generally not sufficiently uniform as regards proportion of fine and coarse material to produce uniformity in the concrete1 and the use of aggregates of that character is not permissible for the wearing course1 but under proper inspection they may be used for the lower course of two course pavements4 ,fine ,aggregate4--,the fine aggregate is generally natural sand1 but a mixture of natural sand and stone screenings is sometimes employed4 ,the fine aggregate of whatever character must be clean1 free from organic matter and sand1 must contain no appreciable amount of mica1 feldspar1 alkali1 shale or similar deleterious substances and not exceed two and one-half per cent of clay and silt4 ,the sand is of such a range of sizes that all will pass the one-fourth-inch sieve and that not exceeding about five per cent will pass the #ajj-mesh sieve4 ,proportions4--,various mixtures for the concrete are employed because these may properly vary to some extent with the exact character and grading of the aggregates4 ,experience seems to have shown that the concrete used for the wearing surface should have a crushing strength of at least #bejj pounds per square inch1 and the mixture adopted is based on the requirements that will give the desired crushing strength4 ,the common mixture for the one course pavement is one part cement1 two parts sand and three and one-half parts coarse aggregate4 ,for the wearing course of the two-course type of pavement1 a mixture of the same kind is very often specified4 ,while these are perhaps the most widely adopted proportions1 many others have been used1 especially where the aggregates exhibit peculiarities or the traffic conditions are unusual4 ,it is desired to emphasize that the purpose is to obtain concrete of the desired strength and there can be no such thing as standard proportions4 ,measuring ,materials4--,in considering the methods employed for measuring aggregates1 emphasis should be placed on the futility of rigid requirements for the aggregates1 both as regards quality and range of sizes1 if the materials are carelessly proportioned at the mixer4 ,if even reasonably near uniform wearing qualities are to be secured throughout the entire area of the concrete road surface1 successive batches of concrete must be alike1 and to insure that1 the aggregates including the water in each batch of concrete must be mixed in exactly the same proportions4 ,the aggregates are measured in various ways1 all essentially alike in that the intent is to insure exactly the same amount of each ingredient for each batch of concrete4 ,one method is to place bottomless boxes in wheelbarrows1 fill the boxes level full and then lift off the box4 ,another is to use a wheelbarrow with a bed of such shape that the contents will be a multiple of #a cubic foot when level full4 ,for the larger jobs1 the aggregates are hauled in industrial cars1 each having sufficient capacity for a batch of concrete4 ,the car body is provided with a partition so as to separate the fine and coarse material4 ,the water is measured in a tank which automatically refills to the same level each time it is emptied and when adjusted for a mixture will introduce the proper amount of water for each batch4 ,it is highly important to use the least amount of water that will produce workable concrete4 ,preparation of the ,earth ,foundation4--,the concrete road is generally placed directly on the natural soil which has been brought to the proper cross section4 ,some engineers advocate that in preparing the subgrade1 the earth be thoroughly rolled2 others prefer not to roll the subgrade4 ,if fills of considerable depth are constructed1 they should either be rolled as built or else should be allowed to settle for some months before the concrete road is placed1 preferably the latter4 ,placing the ,concrete4--,the concrete is placed between substantial side forms of a height equal to the thickness of the concrete road slab at the edge1 and is shaped roughly by means of shovels4 ,various methods have been developed for striking the surface to the exact shape desired and smoothing it4 ,if hand finishing methods are employed1 a plank template is cut to the prescribed cross section and the concrete is shaped by drawing the template along the side forms4 ,sometimes the template is used as a tamper1 being moved along very slowly accompanied by an up and down motion that tends to tamp the concrete4 ,the template is then drawn along a second time to smooth the surface finally4 ,after the surface has been struck off by hand1 it is finally smoothed1 first by rolling crosswise with a slight hand roller about #h inches in diameter and #cj inches long4 ,the final finish is effected by dragging a piece of web belting back and forth across the surface4 ,machines designed to tamp the concrete and strike it off to the required cross section are also employed for finishing4 ,the machine is power operated and is carried on wheels that run on the side forms1 and the machine moves slowly along as the tamping progresses4 ,the concrete is tamped1 struck off to shape and smoothed with the belt at one operation4 ,this method of finishing produces denser and stronger concrete than can be produced by hand finishing methods4 ,placing ,concrete for ,two-course ,road4--,the methods employed for the two-course concrete road are much the same as for the one-course road4 ,the concrete for the lower course is placed and struck off by means of hand tools1 and after that course has progressed a few feet1 the upper course is placed and finished as has been described for the one-course road4 ,curing the ,concrete4--,the setting action of cement is a chemical process1 not merely a drying out of the water introduced in mixing the concrete4 ,the chemical action is progressive for a long time1 but is more rapid during the first few hours than during the later periods1 and the concrete reaches about three-fourths of its maximum strength at the end of seven days4 ,during the setting period and particularly during the first few days1 plenty of water must be available to the cement4 ,to prevent too rapid loss of water from the concrete during the setting period1 the surface must be protected from the wind and sun4 ,this is accomplished by first covering with canvas as soon as the concrete has hardened sufficiently and by later covering with earth1 to a depth of two inches4 ,the earth covering is kept wet for about ten days and is left in place for about one month4 ,in some places the ponding method of curing is adopted4 ,the surface is divided into sections by earthen dikes and the space inside the dikes filled with water to a depth of two or three inches4 ,the water covering is maintained for two weeks or longer4 ,no traffic is permitted on the surface for one month1 and in cold weather traffic may be kept off the surface for a longer period4 ,expansion ,joints4--,to permit the concrete slab to accommodate itself to changes in dimension due to temperature changes1 expansion joints #a_/b inch wide are placed about every thirty feet4 ,these consist of a sheet of some prepared bituminous material placed in position as the concrete is poured4 ,experience seems to indicate that in spite of the expansion joints1 the concrete will crack more or less and many engineers think it advisable to omit expansion joints in constructing the pavement and when cracks develop to pour bituminous material into them1 thus forming expansion joints4 ,the prevailing practice in rural highway construction is to omit the expansion joints1 but they are commonly adopted in city pavements4 ,reinforcing4--,to minimize the cracking1 either bar or wire mesh reinforcing is used in the concrete4 ,if bars are used they are placed in the concrete as it is poured so as to form a belt around each section about #ae feet square4 ,if the mesh type is employed1 a part of the layer of concrete is placed and smoothed off and a strip of the mesh laid in place4 ,additional concrete is then poured on top of the mesh to bring the slab to the required thickness4 ,bituminous ,coatings on ,concrete ,surfaces4--,the concrete road surface is sometimes coated with a layer of bituminous material and stone chips or gravel pebbles4 ,this is particularly advisable where no really satisfactory aggregates are available and the concrete surface would not possess sufficient durability4 ,the bituminous material is applied hot to the surface and is then covered with stone chips or gravel pebbles1 ranging in size from #c_/d inch down to #a_/d inch1 the resulting coating being about #c_/d inch thick4 ,many failures of this type of surface have been recorded due to the difficulty of securing adhesion to the concrete4 ,this seems to be due in part to inability to get the proper bituminous materials and in part to climatic effects4 ,considerable progress has been made in developing this type of surface and it may eventually become a satisfactory maintenance method4 ,characteristics4--,the concrete road is of a granular texture and is not slippery4 ,it is of course rigid and noisy for steel tired vehicles4 ,it is an excellent automobile road and its low tractive resistance makes it a desirable surface for horse drawn vehicles4 ,it possesses a high degree of durability if properly constructed4 ,it is likely to crack indiscriminately but as a general rule the cracks are not a serious defect4 ,maintenance4--,the cracks that appear in the concrete surface are filled once or twice a year1 tar or asphalt being employed4 ,the dust and detritus is cleaned out of the cracks and the hot filler poured in1 with enough excess overflowing to protect the edges4 ,,chapter ,,ix ,,vitrified ,,brick ,,roads ,vitrified brick roads consist of a foundation course of ,portland cement concrete1 broken stone or slag macadam1 or of brick laid flat1 the first named being by far the most generally used1 and a wearing course of vitrified brick4 ,vitrified ,brick4--,vitrified brick are made from clay of such a character that when heated to the required temperature they will fuse into a glassy texture4 ,brick roads are constructed on roads carrying the severest of traffic and the brick must therefore be tough and of high resistance to wear4 ,not all of the clays from which brick may be manufactured will produce a product suitable for road construction1 and paving brick1 even though truly vitrified1 are of different degrees of durability1 depending upon the nature of the clay and the care exercised in the manufacture4 ,paving brick are manufactured by the stiff mud process1 which means that the clay is molded into form in a relatively dry condition4 ,to accomplish this1 considerable pressure is exerted in forcing the column of clay through the dies1 which form the prism from which the brick are cut4 ,if the clay is unsuitable in character or is not properly ground and mixed1 the brick will possess planes of weakness between the various layers of clay which have been pressed together1 and these planes1 called laminations1 are a source of weakness if too marked4 ,it is usual to specify that the brick used for road surfaces shall be free from marked laminations4 ,if the brick is not properly burned it will be only partly vitrified and therefore not of maximum durability4 ,it is customary to specify that the brick shall show a glassy fracture indicating complete vitrification4 ,various defects of a minor nature occasionally develop in the brick during the successive steps in the manufacturing process4 ,check cracks resulting from the burning or from too rapid cooling are often encountered1 but unless these are deep1 that is #c_/af inch or more1 they do not impair the wearing quality of the brick1 nor indicate structural weakness4 ,kiln marks are formed on some of the brick due to the weight of the brick above in the kiln4 ,these depressions are not objectionable unless the brick are so distorted that they will not lie evenly in the pavement4 ,spacing lugs or raised letters are formed on one face of the brick to insure sufficient space between the brick for the filler4 ,these lugs or letters are not less than #a_/h inch nor more than #a_/d inch high and of such design that they will not obstruct the free flow of filler into the joints between the brick4 ,several varieties of paving brick are to be had1 the difference being principally in the design or size4 ,repressed ,brick4--,in this type of brick the spacing lugs are formed by pressing the green brick1 after it has been cut to size1 into a mold on one face of which are recessed letters or other devices into which the clay is pressed1 thus forming the spacing lugs4 ,vertical ,fiber ,brick4--,these brick are designed to be laid with one wire-cut face up and spacing is provided by two or more beads on the side of the brick4 ,sometimes the vertical fiber brick has no spacing lug1 it being contended that the irregularities of the brick are such as to provide all of the space required4 ,in practice this does not always work out1 as the brick are so regular in shape that when laid there is too little space between the brick to permit the introduction of a suitable filler4 ,the use of brick without spacing lugs is just beginning and is not yet a generally accepted practice4 ,wire-cut-lug ,brick4--,this is a type of non-repressed brick which has spacing lugs provided by cutting one face in a special manner which provided lugs for spacing4 ,in this type the wire cut face is the one between the brick as they are laid in the pavement4 ,tests for ,quality4--,the standard test for quality of paving brick is the rattler test4 ,the brick rattler consists of a barrel of #ad sides #bd inches long1 mounted so as to rotate at a speed between #bi4e and #cj4e revolutions per minute4 ,the duration of a test is #ahjj revolutions4 ,ten brick constitute a charge and these are placed in the rattler along with #cjj lbs4 of cast iron spheres4 ,the spheres are of two sizes1 the smaller being #a-g_/h inch in diameter when new1 and the larger #c-c_/d inches in diameter when new4 ,ten of the larger spheres are used and the balance of the charge is made up of the small size4 ,when tested in the standard manner the loss allowable for the several classes of service are as follows3 ---------------------------------------- --- ,maximum ,loss ,traffic ,average ,loss for any ,brick ---------------------------------------- --- ,heavy #bj per cent #bd per cent ,medium #bb per cent #bf per cent ,light #be per cent #bh per cent ---------------------------------------- --- ,other ,tests4--,sometimes the absorption test is specified for paving brick1 but it is rarely a vitrified brick that will pass the rattler tests which fails to pass a reasonable absorption test4 ,absorption of water in an amount exceeding #d per cent indicates incomplete vitrification and failure of such brick is almost certain during the rattler tests4 ,the cross breaking test is also sometimes employed1 but generally only to check the general quality of the brick4 ,failure in service more frequently occurs from excessive wear than from any other cause and the cross breaking test has little significance1 except for brick less than #c inches thick1 which are to be laid on a sand bedding course4 ,foundation4--,the foundation for brick roads is usually of ,portland cement concrete1 the thickness varying with the nature of the traffic and the kind of soil upon which the pavement is built4 ,for well drained soils and normal highway traffic1 #e inches is the ordinary thickness of foundation4 ,under favorable conditions such as locations with sandy soils or in semi-arid or arid regions where the soil is always stable1 the foundation may be four inches thick1 and a considerable mileage of brick road has been built with concrete foundations less than four inches thick4 ,in other locations the soil and traffic conditions require a base six inches or more in thickness1 and the proper thickness can be determined only after all of the factors involved are known and have been analyzed4 ,it is impractical to adopt a standard thickness of foundation that will be equally economical for all locations and all kinds of traffic4 ,as the brick pavement is essentially a heavy traffic type of surface1 the design cannot be varied greatly with similar foundation conditions because the weight of individual loads is the significant factor and this does not vary so much as the volume of traffic4 ,a variation in volume of traffic may be compensated for by a variation in the quality of the brick as already set forth4 ,the mixtures for the concrete foundation vary widely because of the variation in the aggregates employed4 ,if the fine and coarse aggregate for the concrete are of good quality a mixture of one part cement1 two and one-half parts sand and five parts of coarse aggregate would insure concrete of adequate strength4 ,a somewhat leaner mixture is sometimes employed and would be satisfactory if the aggregates were of exceptional concrete making quality4 ,mixtures of sand and pebbles 7unscreened gravel7 may also be used if care is exercised to secure a mixture of adequate strength4 ,the proportion will of necessity vary with each particular material and the discussion of the various considerations involved may be obtained from various standard works on concrete and concrete materials4 ,broken stone macadam is sometimes utilized for the foundation course of the brick pavement and such foundations are constructed as water-bound1 which is described in a previous chapter4 ,the thickness1 like that of the concrete foundation1 varies with the soil conditions and the weight of the loads that are expected to use the road4 ,the macadam is placed in a single layer and is rolled and bonded with screenings as described in the chapter dealing with water-bound macadam4 ,six inches is a common thickness for the macadam base4 ,this type of foundation should be employed only where the soil is quite stable and where material costs are such as to insure that the macadam base is materially cheaper than one of concrete4 ,this would usually be in locations where the cost of cement is high because of long hauls and where suitable macadam materials may be obtained close at hand4 ,old macadam roads are sometimes utilized for the foundation for the brick surface1 but the instances where this is permissible are comparatively few in number4 ,when an old macadam is to be used it is reshaped to the proper cross section and re-rolled and bonded so as to afford a stable foundation of the proper cross slope4 ,,bedding ,,course ,,for ,,brick ,,surfaces ,in order to equalize the variations in size and shape of the brick1 they are laid on a bedding course composed of material into which the brick may be forced by rolling4 ,in this way the upper surfaces of all brick can be brought to the proper elevation to insure smoothness and easy riding qualities4 ,several kinds of bedding course are now employed4 ,sand ,bedding ,course4--,the sand bedding course has been referred to as a sand cushion1 but as a matter of experience the cushion effect is slight1 although sometimes pavements have become uneven because the brick have pushed down into the sand after the pavement was used for a time4 ,the sand for the bedding course should preferably be fine grained1 all particles passing the eight mesh sieve1 but ordinary concrete sand is satisfactory4 ,the sand need not be clean1 as a comparatively large percentage of silt or clay does not impair the usefulness of the material4 ,illustration3 ,fig4 #ai4--;,cross ,sections for ,brick ,highways ,sand ,mortar ,bedding ,course4--,in order to eliminate the tendency for the straight sand bedding course to shift because of the impact of traffic on the brick1 a lean cement mortar is sometimes employed rather than the straight sand4 ,sand and cement in the ratio of one part cement to four or five parts of sand are mixed dry1 and after the brick have been rolled1 is moistened to furnish water to hydrate the cement4 ,the sand employed is ordinary clean concrete sand4 ,green ,concrete ,bedding ,course4--,in the monolithic type of brick road construction1 the brick are laid directly on the green concrete base before the concrete has taken a set and the irregularities of the brick are taken up by rolling them until bedded in concrete4 ,,fillers ,,for ,,brick ,,surfaces ,the spaces between the brick are filled with some material that will prevent the brick from being displaced and prevent water getting to the bedding course4 ,a suitable filler must adhere to the brick and fill completely the spaces between them4 ,it must withstand traffic so as to remain intact in the joints and when in place it must be rigid enough to prevent displacement of the brick4 ,cement ,grout ,filler4--,one of the most commonly used fillers for brick pavements consists of a grout composed of ,portland cement and fine sand4 ,when properly mixed and applied the grout filler meets all requirements for a filler except that it is non-elastic and some means must be adopted for caring for pavement expansion4 ,bituminous ,fillers4--,asphaltic materials and tars are widely used as fillers for brick pavements4 ,such fillers are of high melting point and consequently solid at ordinary temperature4 ,they are poured into the joints hot and when they cool are firm enough to comply with the requirements for a filler4 ,in addition1 they have enough ductility to accommodate the expansion of the pavement due to temperature changes4 ,mastic ,fillers4--,mastic consists of a mixture of about equal volumes of fine sand and a solid bituminous material4 ,the mixture is prepared at high temperature and is worked into the joints between the brick while hot4 ,when cool it resembles the straight bituminous filler except that the mastic is somewhat more resistant to wear than the straight bituminous filler4 ,,expansion ,,joints ,it is recognized that brick will expand and contract with changes in temperature4 ,when a bituminous or mastic filler is employed there is sufficient yield to the filler to accommodate the change in dimension in the brick1 but when the grout filler is used either the expansion joint must be provided or the pavement must be designed to withstand the compression due to expansion of the brick4 ,expansion joints may consist of a sheet of bituminous mastic prepared for the purpose and set in place in the pavement4 ,the sheet of joint material is simply inserted between courses of brick at the proper place4 ,another method of forming an expansion joint consists in placing a strip of wood between courses of brick at the place where a joint is required4 ,after the pavement has been grouted1 the wooden strip is pulled out and the joint is filled with a suitable bituminous filler4 ,marginal ,curb4--,if the sand bedding course is employed1 it is necessary to provide curbing along the sides of the brick to hold the bedding course in place4 ,the curb is usually constructed integral with the base and of concrete of the same mixture as the base4 ,the width of the curb is usually six inches and the top of the curb is at the same elevation as the edge of brick surface4 ,,construction ,,of ,,the ,,surface ,before the construction of a brick surface should be undertaken on a road1 the drainage should be provided for even more completely than for a less costly type of surface since it does not pay to jeopardize the stability of the pavement by failure to provide adequately for the stability of the supporting soil4 ,grades should also be reduced to the economical limit4 ,the earth subgrade is brought to the proper elevation and cross section and is thoroughly rolled4 ,if there are places where the soil will not compact properly under rolling1 these places are corrected by taking out the material and back filling with new material that will properly compact under the roller4 ,the aggregates for the concrete may be distributed along on the prepared subgrade or may be stored in stock piles or bins at convenient points4 ,if stored on the subgrade1 a traction mixer is employed which is drawn along the road as the work progresses1 the materials being placed directly in the mixer4 ,if stored at a central point1 they may be transported to the mixer on the road and dumped directly into the mixer1 or the mixer may be set up at the storage piles and the concrete hauled in trucks to the road where it is deposited and shaped4 ,the concrete is spread to the proper thickness and tamped either by hand or by machinery4 ,if the marginal curb is to be employed1 it is constructed immediately after the concrete for the base has been finished but before the cement begins to set4 ,after the foundation concrete has set1 the bedding course is spread and struck off to the proper thickness4 ,when the bedding course consists of sand-cement mortar1 the sand and cement are mixed dry and spread to prescribed thickness4 ,it is considered to be desirable to roll the sand bedding course with a light hand roller before the brick are placed1 but the sand-cement bedding course is not rolled4 ,the bedding course must be carefully shaped by means of a templet or strike board before the brick are placed4 ,the brick are laid in straight courses across the pavement1 with the spacing lugs all in the same direction if brick with spacing lugs are employed1 and with the lugs in contact with the brick of adjoining courses4 ,if brick without spacing lugs are used they are laid loosely so that there will be room for the filler between the brick of adjoining courses4 ,after the brick have been laid they are rolled to bed them in the sand or sand-mortar bedding course and thus secure a smooth surface4 ,for this purpose a light1 power driven1 tandem roller is used and the rolling is continued until the brick are thoroughly bedded4 ,any defective brick that are noted are removed and replaced with good brick and after this culling has been completed the surface is once more thoroughly rolled4 ,if a cement-sand bedding course is employed1 the surface is sprinkled just after the final rolling so that water will flow down between the brick and moisten the bedding course sufficiently to cause the cement to set4 ,in some cases1 the sand-cement bedding course is sprinkled just before the brick are laid but in warm weather the setting would take place before the brick could be rolled if that were done4 ,in cool weather the setting is sufficiently slow to permit rolling before the bedding course hardens4 ,the filler is applied to the surface after the rolling4 ,if the bituminous type of filler is employed1 the hot filler is poured onto the surface and worked into the joints by means of squeegees1 with comparatively little material left on the surface4 ,in some instances cone-shaped pouring pots are employed and the material is poured directly into the joints4 ,the cement grout filler is applied in the same general manner as the bituminous filler4 ,the grout1 consisting of equal parts of sand and cement1 is mixed to a thin consistency and poured onto the surface and is then worked into the joints with squeegees4 ,two or more applications are usually required to effect a complete filling of the joints4 ,the surface should be covered with sand and be kept moist until the cement grout has set4 ,,chapter ,x ,,bituminous ,,road ,,materials ,,and ,,their ,,use ,tars and asphaltic materials of various kinds are widely used for road construction and maintenance1 especially for road surfaces subjected to motor traffic4 ,materials of this character that are employed in highway work possess varying degrees of adhesiveness1 and while they may be semi-solid or viscous liquids at air temperature1 they melt on the application of heat and can be made sufficiently fluid to mix with the mineral aggregates that may be used in the road surface4 ,upon cooling1 the bituminous materials return to the previous state and impart a certain amount of plasticity to the mixture1 at the same time serving as a binding or cementing agent1 which is sufficiently stable for many classes of road construction4 ,classes of ,bituminous ,materials4--,bituminous materials may be classified1 according to the source from which they are obtained1 as coal tars1 water gas tars1 native or natural asphalts and oil or petroleum asphalts4 ,coal ,tar4--,coal tar is obtained as a by-product in the manufacture of illuminating gas from coal4 ,it is also obtained in the manufacture of coke from coal4 ,the tar thus obtained is manufactured into products that are used for dust layers on gravel or macadam roads1 binders for macadam and gravel surfaces1 fillers for brick1 wood block and stone block pavements and for expansion joints4 ,these various materials differ mainly in their consistency at air temperature4 7,they may differ widely in chemical composition1 but that need not be considered herein47 ,water ,gas ,tar4--,water gas tar is obtained as a by-product in the manufacture of illuminating gas from crude petroleum4 ,it is used for the same kinds of construction as coal tar1 and the products utilized for the several purposes1 like the coal tars1 differ mainly in consistency4 ,natural ,asphalt4--,natural asphalt is found in deposits at many places in the world1 existing in beds or pools where it has exuded from the earth or as veins in cavities in the rocks4 ,it is of varying composition and consistency1 but those kinds in most general use are solid or very viscous liquids at air temperature4 ,of the deposits that have been developed on a commercial scale1 the ,trinidad lake in the ,british ,west ,indies and ,bermudez deposit in ,venezuela are best known4 ,both of these materials are too hard in the natural state to be used for road construction1 and are softened1 or fluxed as it is called1 with fluid petroleum oil before being used4 ,petroleum ,asphalt4--,petroleum asphalt is a residue remaining after the fluid products have been distilled from petroleum4 ,residues of this sort are not always suitable for road construction1 but a number of brands of road material are obtained from this source4 ,oil asphalts are used for dust layers1 for binders for macadam roads1 for asphalt cements for sheet pavement surfaces1 and for fillers for block pavements and expansion joints4 ,mixtures4--,water gas tars and asphalts are sometimes mixed to produce road materials1 and likewise native asphalts and residues obtained from petroleum are sometimes mixed to produce asphalt cements for paving mixtures4 ,classification according to ,consistency4--,the various bituminous materials may be classified according to consistency in discussing the various uses to which they may be put4 ,road ,oils4--,road oils are fluid petroleum oils of such consistency that they may be applied cold or by heating slightly4 ,they are used as dust layers on earth1 gravel and macadam surfaces4 ,their efficacy depends upon the binding properties of the small amount of asphaltic material that is contained in the oil4 ,liquid ,asphalts4--,these are somewhat less fluid than the road oils1 and must always be heated before application1 but are viscous liquids at ordinary temperature4 ,these materials are obtained from crude petroleum or semi-solid native bitumens1 in which case they are usually called malthas4 ,both coal tars and water gas tars of semi-solid consistency are also employed for the same class of construction as the liquid asphalts4 ,these materials are used for carpeting mediums on macadam roads and as cementing agents in the construction of hot-mixed macadam4 ,asphalt ,cements4--,the solid asphaltic materials used for hot-mixed types of construction are called asphalt cements4 ,they may be petroleum residues or native asphalts fluxed with petroleum oils4 ,they are solids at ordinary temperature and must be heated to a temperature in excess of two hundred and fifty degrees before they are sufficiently fluid to use4 ,asphalt cements are used for sheet asphalt and asphaltic concrete construction and for hot-mixed bituminous macadam4 ,fillers4--,fillers are solid asphalts or tars that are used for filling expansion joints in rigid pavements and for filling the spaces between the blocks in brick1 wood block and stone block pavements4 ,bitumen4--,bituminous materials are all soluble to a greater or lesser extent in carbon disulphide and the soluble portion is called bitumen4 ,it is the bitumen that gives to the materials the cementing properties utilized in road construction4 ,mixtures of mineral aggregates and bituminous materials for various purposes are proportioned with bitumen as a basis4 ,therefore1 less of an asphalt containing one hundred per cent bitumen will be used than of one containing less than one hundred per cent of bitumen4 ,,table #h ,,properties ,,of ,,asphaltic ,,road ,,materials 7,a7 ,material 7,b7 ,specific ,gravity 7,c7 ,consistency 7,d7 ,solubility in ,,cs#b1 ,per ,cent 7,e7 ,solubility of ,bitumen in ,c,cl#d1 ,per ,cent 7,f7 ,solubility of ,bitumen in #hf ,naphtha1 ,per ,cent 7,g7 ,fixed ,carbon1 ,per ,cent 7,h7 ,flash ,point 7,i7 ,ductility ---------------------------------------- -------------------------- 7,a7 7,b7 7,c7 7,d7 7,e7 ---------------------------------------- -------------------------- ,mexican oil asphalts #a4jc-a4je;,as desired #ii4e-ii4iii4e-ii4i ,california oil asphalts #a4jb-a4jd;,as desired #ii4i #ii4i ,texas oil asphalts #a4ja-a4jc;,as desired #ii4i #ii4i ,bermudez natural asphalt#a4jg #be #ie #ii ,trinidad natural asphalt #a4dj #g #ef-eg #ajj ,bermudez asphalt cement #a4jd-a4jf,up to #ace #ie-ig #ii4e or more ---------------------------------------- -------------------------- ---------------------------------------- -------------------------- 7,a7 7,f7 7,g7 7,h7 7,i7 ---------------------------------------- -------------------------- ,mexican oil asphalts #gj-hj #ac-af #bjj;,c4 up #fj-ajj ,california oil asphalts #ge-hj #aj-ab #bjj;,c4 up #ajj ,texas oil asphalts #ge-hj #ab-ad #bjj;,c4 up #ej-ajj ,bermudez natural asphalt #fh-gj #ac-ad 444 444 ,trinidad natural asphalt #fd-fe #aj-aa 444 444 ,bermudez asphalt cement #gg-hj #aa-ab #age-bjj #be-ej ---------------------------------------- -------------------------- ,specifications4--,some properties of bituminous materials can be varied in the process of manufacture1 while others are inherent in the material and cannot be changed in the process of manufacture4 ,specifications must therefore be drawn with care to insure that the requirements can be met by satisfactory materials4 ,but certain properties1 such as specific gravity1 may vary greatly among materials equally satisfactory for construction purposes4 ,one should not be misled by apparent differences in the characteristics of materials1 because these may simply be natural peculiarities which have no bearing on the usefulness of the material4 ,there are given in ,table #h the properties of some of the commonly used bituminous materials and the properties that can be varied in the process of manufacture are indicated with an asterisk4 ,a variation in these properties will usually result in some change of other properties1 but generally not a great change4 ,,surfaces ,,in ,,which ,,bituminous ,,materials ,,are ,,utilized ,i4 ,surface ,treatments ,attention has been directed to the rapid deterioration of water-bound macadam when subjected to passenger automobile traffic4 ,in water-bound macadam the stones are held in place by a weak cement composed of stone dust and water1 and this cement is not sufficiently strong to hold the stones in place when they are subjected to the shear of automobile tires4 ,in finishing the water-bound macadam surface1 the spaces between the stones are filled with screening and in addition a layer about one-fourth inch thick is left on the surface4 ,the automobile traffic first brushes aside all of the screenings and smaller particles of rock1 exposing the larger stones4 ,these gradually loosen as the road is used and are brushed aside4 ,when this effect begins1 the road is said to be raveling4 ,various lengths of time may elapse from the time the road is first finished until raveling begins1 depending upon the character of the stone1 the weather and the amount of motor traffic4 ,during the period before raveling starts1 it is comparatively easy to restore the road surface at any time by the addition of screenings or clay and sand4 ,usually there will be a few small areas of the surface that1 on account of faulty construction1 will ravel or become rutted much earlier than the remainder of the surface4 ,these can be repaired by the methods described in the chapter on ,water-bound ,macadam ,construction4 ,when the surface begins to ravel seriously1 maintenance becomes much more difficult and in order to prevent raveling and the difficulties of maintenance thereafter1 the macadam surface is often coated with a bituminous material4 ,illustration3 ,fig4 #bj4--,oiling a ,gravel ,road ,if there is any dust or screenings on the road surface1 the bituminous material will not adhere to the stones and will soon flake off under traffic4 ,the surface of the macadam must therefore be thoroughly cleaned before the bituminous material is applied4 ,the usual practice is to finish the road as water-bound macadam1 and permit traffic on it for a sufficient length of time to show any weak places in the surface and at the same time thoroughly to season the surface4 ,if any defective places appear1 they are repaired and when the surface exhibits satisfactory stability1 but before it begins to ravel1 the bituminous surface is applied4 ,there will ordinarily be some stone dust and some screenings remaining on the surface at the time bituminous treatment is undertaken1 and there may also be some caked mud or other foreign material4 ,all of this must be removed so as to expose the stones throughout4 ,applying the ,bituminous ,binder4--,the bituminous binder may be delivered in tank cars1 which is desirable if the work is near a railroad siding1 or ample tank wagon service is available for long hauls so that the tank will not be held up too long4 ,often it is desirable to purchase the binder in barrels and haul these to the site of the work in advance of beginning the construction of the surface4 ,the bituminous material may be applied by means of hand spreading cans not unlike an ordinary garden watering pot1 except that a slotted nozzle is substituted for the ordinary perforated one4 ,if hand methods are employed for spreading1 the bituminous material is heated in open kettles and then spread on the surface1 the quantity required usually being about one-half gallon per square yard of surface4 ,the temperature of the binder should be great enough to insure fluidity and the road should be dry at the time of the application4 ,as soon as the material has been spread1 the surface is finished with a dressing of chips4 ,finishing the ,surface4--,for surface dressing the best material is stone chips ranging in size from about #a inch down to one-fourth inch4 ,but the chips must be of durable material1 or they will quickly grind into dust4 ,they must be free from dust when applied1 as the presence of any considerable amount of dust interferes with the proper finishing of the surface4 ,the stone chips are rolled into the surface1 a sufficient quantity being used to just cover the surface4 ,patching4--,it almost always happens that some small areas will not be properly cleaned or that for some unknown reason the coating peels off the surface4 ,such places must be promptly patched to prevent them enlarging under the action of traffic4 ,this work is usually done by patrolmen1 who inspect the road at frequent intervals and make the necessary repairs4 ,the patrolman is equipped with a small heating kettle1 a spreading can and the necessary brushes1 tampers and miscellaneous tools needed for the repair work4 ,the place to be patched is carefully cleaned1 coated with bituminous binder and stone chips and tamped until dense and solid4 ,repairs made in this way are exceedingly important in that they arrest deterioration in its early stages and maintain a high degree of serviceability4 ,,ii4 ,penetration ,macadam ,a considerable mileage of macadam has been constructed in which an attempt was made to eliminate the difficulties of maintenance by a method of construction that involves applying a bituminous binder in such a manner as to permit it to penetrate two inches or more into the surface4 ,it is expected that the binder will coat the stones to such an extent as to increase materially the stability of the bituminous macadam over the surface treated one4 ,it is also expected that less difficulty will be encountered in maintaining a surface of bituminous material and stone chips on this type of road than on the water-bound macadam4 ,the extent to which these expectations have been realized has varied to a marked degree and although some excellent surfaces have been constructed by this method1 the results have as a rule been neither uniform nor entirely satisfactory4 ,it seems to be apparent that good results cannot be obtained unless the materials are entirely suitable and the construction is carried out with unusual skill4 ,foundation4--,the foundation or lower course consists of a layer of broken stone six inches thick placed on a well drained and thoroughly rolled earth subgrade4 ,in exceptional cases1 the ,telford type of foundation might be employed4 ,the lower course of broken stone is finished in the same manner as water-bound macadam1 being bonded with stone screenings or with fine gravel of high clay content4 ,since this course is in reality the foundation of the surface1 it is necessary to secure stability by appropriate construction methods1 exactly as in constructing water-bound macadam4 ,illustration3 ,fig4 #ba4--,type of ,roller used on ,gravel and ,macadam ,roads ,upper or ,wearing ,course4--,the wearing course consists of a layer of stone about two and one-half inches thick4 ,the stone is placed and rolled and the spaces between the stones partially filled with some suitable bituminous material4 ,the bituminous material is usually applied by means of a mechanical spreading device connected to a tank wagon4 ,the bituminous materials employed for this class of construction are semi-solid in character and must be heated to give them sufficient fluidity for application4 ,they may be heated in the tank wagon which is used for the application or they may be heated in separate tanks and transferred to the distributing wagon for spreading4 ,some kind of a nozzle or group of nozzles is employed for spreading the material so that it can be delivered in the form of a spray or at least in a thin fan-shaped stream and can be distributed in a fairly uniform layer over the stone4 ,the binder will cool rather rapidly after it is applied1 but meanwhile will flow into the openings between the stones and will form over the surface stones a coating of slight thickness4 ,the surface of the macadam is next covered with a layer of chips of tough rock1 similar to the material used for the final dressing in surface treatments4 ,these are carefully brushed into the openings between the larger stones by means of heavy brush brooms4 ,this is an exceedingly important part of the work and often a much neglected part of the construction4 ,the surface is then covered with a second application of bituminous material1 somewhat less in quantity than required for the first treatment and the surface again covered with stone chips and brushed4 ,the surface is then thoroughly rolled and is ready for traffic4 ,patching4--,as in the case of surface treatments1 there are likely to be places that1 on account of defects in the construction1 will fail soon after the road is placed under traffic4 ,these will quickly enlarge unless they are repaired promptly4 ,the repairs are made by loosening the stone in the area affected and adding new stone as needed and then pouring on the necessary amount of bituminous material to coat the stones4 ,allowance must be made for the compression of the material by tamping so that a depression does not result4 ,the stones are carefully tamped to place and covered with chips which are also tamped4 ,characteristics4--,the penetration macadam is a surface well adapted to motor traffic if the individual vehicles are not too heavy4 ,it is likely to squeeze out of shape under motor truck traffic1 becoming seriously uneven and uncomfortable for traffic4 ,its durability is materially affected by the construction methods followed4 ,,iii4 ,hot ,mixed ,macadam ,the wearing course of the mixed macadam is composed of graded broken stone or gravel and a bituminous binder4 ,usually the bituminous material only is heated prior to the mixing1 but sometimes the stone is also heated4 ,foundation4--,the lower course1 which serves as the foundation1 is either broken stone macadam1 gravel or concrete4 ,where a foundation of broken stone is used1 it is constructed of the materials and in the manner described for the foundation of the penetration macadam4 ,quite often a badly worn macadam or gravel road is used for the foundation and a new wearing course provided by adding a mixed macadam surface4 ,if such is the case1 the old surface is worked over so as to restore the shape sufficiently and to insure that it is everywhere of sufficient thickness4 ,portland cement concrete is sometimes used as a foundation for the mixed macadam1 but not often4 ,usually if the traffic is of a character requiring a concrete foundation1 it is desirable to use a better wearing course than the mixed macadam1 and the asphaltic concrete or sheet asphalt type of surface is employed4 ,it is necessary to finish the surface of the concrete base with some device that will leave the surface rough to prevent the macadam from creeping4 ,a knobbed tamper which leaves numerous irregular depressions about #b inches in diameter and three-fourths inch deep is often employed4 ,sizes of ,stone4--,for the wearing surface1 stone ranging in size from #b inches down to one-fourth inch is usually employed4 ,if the stone is of good quality the maximum size may be but #a-a_/b inches1 but soft or even medium stone of that size are likely to crush under traffic4 ,the stone for the base course should preferably be from #c inches down1 but any available size will be satisfactory if the layer is well rolled and bonded4 ,the base course is constructed in the same manner as water-bound macadam and any material satisfactory for the base course of macadam will serve for the base course of mixed macadam4 ,screenings having good bonding properties will also be required for the base course4 ,mixing and ,wearing ,surface4--,several methods are employed in mixing the wearing surface4 ,the simplest is to mix by hand with shovels4 ,the aggregates are heated in improvised heaters which may consist of nothing more than a metal pipe two or three feet in diameter1 around which the stone is piled4 ,the mixing platform is usually a metal plate sometimes arranged so that it can be heated by means of a fire underneath4 ,the bituminous material is heated in kettles4 ,for some mixtures1 the stone is not heated1 but the bituminous material is always heated4 ,the batch of stone is placed on the mixing platform1 the bituminous material added and the materials mixed by hand4 ,machine mixing is practiced much more extensively than hand mixing1 being both more rapid and cheaper4 ,the mixer is similar to a concrete mixer except that the drum is arranged so that it can be heated4 ,the hot stone and the bituminous binder are put into the drum and mixed for the requisite length of time4 ,sometimes the stone is mixed cold1 the bituminous material only being heated4 ,placing the ,wearing ,surface4--,the hot mixture is carted to the road and spread to such thickness that after rolling the wearing surface will be not less than two inches thick4 ,the hot mixture is dumped and then spread by means of shovels to the approximate thickness and the spreading completed by means of rakes4 ,the surface is then rolled either with a tandem or a three-wheeled roller until thoroughly compressed4 ,seal ,coat4--,after the rolling has been completed1 the surface is covered with hot bituminous cement and dressed with pea gravel or stone chips and again rolled4 ,traffic may be permitted in twenty-four hours4 ,characteristics4--,the mixed macadam is a somewhat resilient surface of excellent riding qualities and considerable durability for medium traffic4 ,it is likely to creep and become uneven when subjected to heavy loads4 ,the seal coat will wear off in two or three years and will require replacing4 ,,iv4 ,asphaltic ,concrete ,asphaltic concrete is a name given to a road surface mixture which is composed of graded stone1 graded sand and asphalt cement4 ,this type is designated as asphaltic concrete because of the analogy of the mixture to ,portland cement concrete4 ,asphaltic concrete is of two general types known as bitulithic1 or ,warrenite1 and ,topeka asphaltic concrete1 respectively1 the differences being in the nature of the mixture4 ,bitulithic or ,warrenite4--,the stone employed for these types is graded down from a size about equal to one-half of the thickness of the wearing course1 and stone passing a #a-a_/d or #a-a_/b-;inch screen is usually specified4 ,from the maximum size the stone is graded down to the finest particles produced by the crusher4 ,the range of sizes of stone will vary with the source of the supply1 and in order to secure the desired density in the mixture1 varying amounts of graded sand and mineral dust1 such as ground limestone or ,portland cement1 are added to the broken stone4 ,usually the resulting mixture contains less than fifteen per cent of voids1 and to this carefully graded mineral aggregate there is added enough asphalt cement to bind together the particles4 ,topeka ,asphaltic ,concrete4--,in this type of asphaltic concrete1 the mineral aggregate consists of a mixture of carefully graded sand and of broken stone of such size that all will pass a one-half-inch screen and graded down to the fine dust produced by the crusher4 ,to this mixture is added about nine per cent of ,portland cement or limestone dust4 ,the voids in the mixture are usually about twenty-five per cent4 ,it will be seen that the essential differences between the ,bitulithic and ,topeka types are these3 the ,topeka type contains a larger percentage of voids and stone of a smaller maximum size than the ,bitulithic4 ,both types have been extensively employed for city paving1 but the ,bitulithic and ,warrenite types have also been used to some extent for rural highways4 ,the ,topeka type has been used but little for rural highways4 ,foundation4--,the foundation for the asphaltic concrete may be an old macadam road1 a base course constructed of broken stone or ,portland cement concrete1 the latter being used much more extensively than either of the other types4 ,sometimes asphaltic concrete is used for resurfacing water-bound macadam or gravel roads when the traffic has increased to the point where the cost of maintenance of the water-bound macadam has become excessive4 ,the existing surface is repaired and the cross section is restored1 or possibly flattened somewhat4 ,placing the ,surface4--,the stone1 sand and asphalt cement are heated to the required temperature and combined in the proper proportions and are then thoroughly mixed by a mechanical mixer4 ,the mixture is hauled directly to the road and is dumped and spread by means of rakes4 ,it is then rolled thoroughly while still hot1 a three-wheeled roller being most satisfactory4 ,after rolling1 a seal coat of hot asphalt cement is spread over the surface and covered with hot stone chips about #a_/d inch in size4 ,the surface can be opened to traffic immediately after the surface has been completed4 ,characteristics4--,the asphaltic concrete surface is of excellent riding properties1 is easily repaired and of moderate durability4 ,it is a particularly desirable surface for pleasure automobile riding and for horse drawn traffic4 ,,chapter ,,xi ,,maintenance ,,of ,,highways ,proper maintenance of highways is equally important with proper construction4 ,with nearly all types of road construction1 the need for maintenance arises soon after the surface is placed under traffic and is continuous thereafter4 ,the nature and amount of maintenance work varies greatly among the several types of surface and the organization suitable for a system of highways will depend to a considerable extent upon the kinds of surfaces that are to be maintained4 ,the upkeep of a road may be conveniently considered as of two kinds1 viz41 7#a7 that which has to do with the wearing surface and earth shoulders or berms upon which there is some traffic and 7#b7 that which has to do with the side ditches and drainage structures and keeping the roadside in presentable condition4 ,both kinds of work are usually carried out by the same organization1 but whereas the nature of the work indicated under 7#a7 will vary with the type of wearing surface and with all variations in traffic1 that which is indicated under 7#b7 will be nearly constant in any locality4 ,,organization ,,for ,,maintenance ,maintenance of highways is preferably under the administration of the same authority as construction and when an improvement is undertaken under the jurisdiction of a ,state ,highway ,department1 the completed improvement is ordinarily maintained under the state authority4 ,if the improvement is made by county authorities1 the maintenance is also carried out under county authority4 ,the nature of the organization of maintenance forces is dependent upon the kind of roads to be cared for and must of necessity be varied in any instance as conditions demand4 ,in general1 either maintenance gangs or patrolmen are employed and often both are used on the same road system4 ,patrol ,maintenance4--,where this system is in operation1 the highway system is divided into patrol districts of from six to eighteen miles of highway and a single patrolman is placed in charge of each district4 ,he is provided with all of the necessary tools and materials required in his district and performs all of the work required in the ordinary upkeep of the highway4 ,he should work under the direction of the county engineer or the district engineer for the state highway department1 because his work involves the use of materials and processes requiring technical supervision4 ,gang ,maintenance4--,the maintenance gang may be employed for some types of road surface in lieu of the patrolman or with other types of surface may be employed to supplement the work of the patrolman4 ,the maintenance gang consists of three to ten men and is furnished all of the tools and materials required for the particular kind of work they do4 ,ordinarily the gang goes over the roads assigned to it once each season and performs those repair operations requiring more work than the patrolman can find time for4 ,the work of the maintenance gang like that of the patrolman should be under engineering supervision4 ,maintenance of ,earth1 ,sand-clay1 ,gravel and ,macadam ,roads4--,the ordinary upkeep of earth1 sand-clay1 gravel and macadam surfaces is most readily accomplished by the patrol method1 since constant care is required to keep the roads in a condition of maximum service ability4 ,the tools required for each patrolman may include the following3 #a shovel #a spade #a stone rake #a pick #a scythe #a tamper #a or more road drags #a mowing machine for cutting weeds #a wheelbarrow 7sometimes7 #a light truck #a small kit carpenter's tools ,the work of the patrolman consists in keeping the surface of the road smooth by dragging1 repairing chuck holes by tamping in fresh material of the appropriate kind1 keeping the ditches and culverts free from obstruction1 cutting weeds and repairing bridge floors if they are of plank construction4 ,removal of snow drifts is sometimes a part of the patrolman's duty1 but more often that is done by special gangs4 ,usually the patrolman is authorized to hire teams for dragging and cutting weeds4 ,when an earth road requires to be re-graded so as to restore the cross-section and deepen the ditches1 a gang is sent in to perform that work1 as it is obviously impossible for the patrolman to perform work1 of that kind4 ,if the gravel road is being maintained with a bituminous carpet coat1 the patrolman will be furnished the necessary tools to enable him to patch the surface with bituminous material as necessity requires4 ,when the surface deteriorates to such an extent that a new carpet coat is required1 the gang system is employed for all work connected with resurfacing1 instead of attempting to have the work done by patrolmen4 ,the maintenance of the macadam road is carried out in much the same manner as that of the gravel road4 ,the binder of stone dust or clayey sand is renewed as often as it is swept off by traffic4 ,depressions or ruts are repaired by first loosening the surface with a pick and then adding broken stone and screenings to restore the surface4 ,when the macadam reaches the stage where entire resurfacing is needed1 the work is performed by gangs organized and equipped for the purpose2 and likewise when the surface is being maintained with a bituminous carpet1 the renewal of the carpet coat is performed by special gangs1 but the ordinary upkeep of the surface by patching is handled by a patrolman4 ,,maintenance ,,of ,,mixed ,,bituminous ,,surfaces ,illustration3 ,fig4 #bb4--,scarafier used in ,gravel ,road ,maintenance ,these types of surface can be kept in satisfactory condition if they are carefully repaired once or twice each season4 ,this work requires considerable experience and some special equipment1 not ordinarily supplied to patrolmen4 ,a gang is organized for the work and supplied with the proper equipment4 ,they go over the roads and patch all worn places1 generally first removing the wearing surface entirely in the area affected4 ,the wearing surface mixture is then prepared and tamped or rolled into place4 ,if the area affected is small1 tamping is satisfactory1 and when the area is considerable1 rolling is employed4 ,the upkeep of the side roads may be accomplished by the same gang but is preferably taken care of by patrolmen1 who do not attempt any but minor repairs to the wearing surface4 ,,maintenance ,,of ,,brick ,,and ,,concrete ,,roads ,on brick and concrete roads1 the principal work on the wearing surface consists in filling the cracks with a suitable bituminous material4 ,this work is done by patrolmen or by special gangs and generally will be done once each year4 ,the upkeep of the side roads is cared for by patrolmen who drag the side roads and cut the weeds as occasion requires4 ,,index ,administration county2 #ae federal2 #ag highway2 #ac state2 #af township2 #ac ,aesthetics2 #fb ,aggregate1 fine2 #aja ,aggregate1 coarse2 #ajj ,air resistance2 #ea ,alignment2 #df ,applying bituminous binder2 #abb ,asphaltic concrete2 #abh ,asphalt1 natural2 #aag liquid2 #aah petroleum2 #aag ,assessments1 special2 #ai zone method2 #bj ,bedding course1 green mortar2 #aaa sand mortar2 #aaa sand bedding mortar2 #aaa ,binder for gravel2 #ge ,bitulithic or warrenite2 #abh ,bitumen2 #aah ,bituminous coatings on concrete2 #aje ,bituminous fillers2 #aab ,bituminous road materials and their use2 #aaf ,bituminous surfaces2 #if1 #abj ,blade grader2 #fi ,bonding2 #hg ,bonds1 annuity2 #bf serial2 #bg sinking fund2 #be ,box culverts2 #ci ,brick roads2 #aac ,brick1 repressed2 #ajg tests of #ajh2 vertical fiber2 #ajg vitrified2 #ajf wire-cut-lug2 #ajh ,broken stone road surfaces2 #hi ,cement1 asphaltic2 #aah ,cement concrete roads2 #ih ,cement grout filler2 #aab ,characteristics1 asphaltic concrete2 #abi bituminous macadam2 #abe broken stone2 #ig concrete2 #aje mixed macadam2 #abh sand clay2 #gh ,classes of bituminous materials2 #aaf ,classification according to consistency2 #aag ,clay and cement concrete pipe2 #ci ,coal tar2 #aaf ,concrete1 asphaltic2 #abh ,concrete materials2 #ajj ,concrete pipe2 #ci ,control of erosion2 #fa ,costs2 #gj ,county administration2 #ae ,cross sections2 #fj1 #fe ,culverts2 #ef ,curing concrete2 #ajc ,design1 broken stone roads2 #hi concrete roads2 #ii earth roads2 #db ,desirability of road bonds2 #bg ,development of traffic2 #b ,drainage1 necessity of2 #bi ,drainage of roads2 #bi ,earth roads1 in arid regions2 #gb humid regions2 #fe value of2 #gc ,earth works2 #ib ,education1 rural2 #f ,effect of grades2 #ed ,elevating grader2 #ff ,elevating grader work2 #fh ,end walls for culverts2 #ci ,energy loss on account of grades2 #eg ,entrances1 farm2 #cg1 #fa ,expansion joints2 #ajd ,farm entrance culverts2 #cg ,federal administration2 #ag ,fillers2 #aah ,finance1 highway2 #ai ,fine aggregate2 #aja ,finishing surface of concrete2 #abb ,foundation1 asphaltic concrete2 #abi brick2 #aji macadam2 #ic mixed macadam2 #abf penetration macadam2 #abc ,telford2 #id ,gang maintenance2 #aca ,grader1 ,maney2 #fg use of2 #fi ,gravel1 ideal2 #ha natural2 #hc roads2 #gd ,general taxation2 #bd ,good roads and commerce2 #g ,green concrete bedding course2 #aaa ,highway administration2 #ac ,highway finance2 #ai maintenance2 #acj ,importance of design2 #cj ,ideal road gravel2 #ha ,inter-city traffic2 #e ,inter-county and inter-state traffic2 #e ,internal resistance2 #ej ,intersections2 #df ,laying tile2 #ce ,length of culvert2 #cg ,liquid asphalt2 #aah ,local farm to market traffic2 #d ,macadam2 #hi ,maintenance1 concrete2 #aje earth roads2 #gj general2 #aca gravel roads2 #hh macadam2 #if of highways2 #acj patrol2 #aca ,maney grader2 #fg ,marginal curb2 #aac ,measuring materials2 #aja ,metal pipe2 #ch ,mixing wearing surface2 #abg ,mixtures2 #aag ,natural asphalt2 #aag gravel2 #gi ,necessity for planning2 #db drainage2 #bi ,patching2 #abb1 #abe ,patrol maintenance2 #aca ,pebbles1 size of2 #hj ,petroleum asphalt2 #aag ,placing asphaltic concrete2 #abi ,placing broken stone2 #id ,placing concrete2 #ajb1 #ajc mixed macadam2 #abg ,plans for roads2 #dc ,preliminary investigation2 #dd ,preparation of earth foundation2 #ajb of road2 #he ,private entrances2 #fa ,properties of stone2 #ij ,proportions for concrete roads2 #aja ,purpose of highways2 #a ,reinforced concrete box culverts2 #ci ,reinforcing2 #ajd ,repressed brick2 #ajg ,road oils2 #aag ,road plans2 #dc ,rocks1 kind of1 for macadam2 #ia ,rolling1 macadam2 #ie ,rolling resistance2 #ej ,run-off2 #ca ,rural education2 #f ,rural social life2 #g ,safety consideration2 #eh ,sand bedding course2 #aaa ,sand clay and gravel road2 #gd ,sand mortar bedding course2 #aaa ,seal coat2 #abg ,serial bonds2 #bg ,sinking fund bond2 #be ,slip scraper2 #fg ,special assessments2 #ai ,specifications2 #aai ,spreading screenings2 #ie ,state administration2 #af ,stone1 use of2 #ib ,surface drainage2 #cj ,surfaces1 bituminous2 #abj ,surface method2 #hg ,superelevation2 #dg ,tests1 brick2 #ajh ,tile drains2 #ce ,topeka asphaltic concrete2 #abh ,tractive resistance2 #eb ,trench method2 #he ,truck operation costs2 #i ,types of culverts2 #ch ,underground water2 #cd ,undulating roads2 #eh ,use of blade grader2 #fi ,utilizing natural gravels2 #hc ,value of earth roads2 #gc ,variation in rainfall2 #fd ,variation in soils2 #fc ,vehicle taxes2 #bd ,vertical fiber brick2 #ajg ,vitrified brick roads2 #ajf ,vitrified brick2 #ajf ,water gas tar2 #aag ,width of roadway2 #ei ,wire-cut-lug brick2 #ajh ,zone method of assessing2 #bj 99 99 99 99 99 ,transcriber's ,notes3 ,the transcriber made these changes to the text to correct obvious errors3 #a4 p4 #e1 accomodate -- accommodate #b4 p4 #ci1 guage -- gauge #c4 p4 #df1 enbankment -- embankment #d4 p4 #fc1 tought -- tough #e4 p4 #fh1 absorbant -- absorbent #f4 p4 #gc1 persistant -- persistent #g4 p4 #gg1 indispensible -- indispensable #h4 p4 #aai1 aspealt -- asphalt #i4 p4 #abg1 repaid -- rapid #aj4 p4 #acj1 ,vetrified brick2 #aje -- ,vitrified brick2 #ajf #aa4 p4 #acj1 ,virtical -- ,vertical ,end of ,transcriber's ,notes