Show lt LOCATION AND DESIGN OF 01 VARIOUS ROADS irlo C lo 10 ajol donihe rals of and arwe 0 CROSS SECTION SOMETIMES USED ON SIDE HILL CURVES TO PREVENT OF VEHICLES AND EROSION OF THE SLOPES rio 2 of hs n 00 jq I 1 CROSS SECTION BOM BEHM DIWI BUILT ABOVE SLOPE SW is of the ditch tot are eily by the or of water waler to bo carried generally ato aj 0 abo ar prepared by the united states spart department of agriculture the minimum width to accommodate safely two lines alnea of average horse drown drawn traffic Is 14 feet and for automobile traffic the width preferably should be not less than 18 feet though a width of 10 feet Is used frequently iu in norderto order to maintain the traveled way to the required width and to afford proper safeguards against accidents it Is necessary a shoulder not less than three or four feet wide along each lidit of thoP roadway proper the shoulders may have a somewhat steeper crown than the rest of 0 the road surface but they should bo be sufficiently flat not to endanger traffic using them and really should constitute an additional width of roadway this means that tunit the total width of roadway between side ditchey ditches never should bedess bo less than 20 feet where horse drawn traffic predominates and 24 feet reany any considerable volume of altol autol automobile bile truffle traffic Is to be accommodated where sharp curves occur in the alignment it to la desirable though not customary to increase the width of the traveled way A A vehicle being drawn along a curved road tends to occupy an appreciably greater width than where the road is straight and unless the width of the traveled way Is increased correspondingly this tendency contributes materially to the hirv hazards ards that invariably accompany sharp curves the minimum widths given above should also be increased 0 on embankments of any const considerable demable depth so as to make maintenance easier and at the same time diminish the danger of accidents the width of right of way required to provide all necessary area for the roadway slopes and ditches varies considerably with the nature of the topography oradea grades in desiring designing a public road one of the most difficult problems to properly ls is the question of maximum allowable grades in deciding this question the advantages advantage to be gained by reducing oil all of the steeper grades on apar a particular road to a given maximum should be weighed against the additional cost which the reduction in volver lyes the following data and bugge suggestions scions ate intended to aid individual judg intent necess necessarily airily must be the prime factor in solving this important emblem blem 1 the cost of average pleasure trat mc fie horse drawn and motor Is roily rally unaffected by grades of lotmore not more than 6 or 7 per cent six or seven feet line per feet Inea measured horizontally provided the conditions are such that it Is unnecessary to apply the blakes to vehicles when descending the grades but tor for traffic where loads are as important as speed even light grades may be of considerable disadvantage 2 increasing the steepness of a grade decreases la in three distinct ways the load a n horse can haul a for the same cume character of surface ethe the required ti active effort or pull per ton of load Is increased by about 20 pounds for each percent per cent increase in grade b the possible pull the horse can exert la is decreased by an amount equalito equal to the effort required to lift his own weight through the rise this amount li 19 approximately equal to one one hun dreith of the horses weight for each per cent increase in grade c the effective bullof pull 0 the horse Is reduced reduce dby by the change in the angle at which the pull is 1 apall applied ed 8 the pull a horse can exert on a levil level road varies variel greatly with the in dIvId lial animal and Is affected by the of hitching and the skill of the driver the character of the road surface also may have an important influence by affecting the security of the horses foothold bold tests teits made by the office of public roads and rural engineering indicate that on a level road average farm horses untrained to the road cart can exert ti it steady pull for several consecutive hours houra equivalent to from OOS to of bleir own weight i without undue fatigue and th that at by resting at inter valsom from to GOO feet they can call exert a pull equivalent to fo about oc provided the foothold la in good 4 the tests referred to above also Ind indicate lente that with a well constructed wago the pull required to move a gross rosa load of one ton over a leyel level road varies about as follows pounds loose sand band road i average dry earth road varied greatly lit atly ly i i W finn earth arth or sand band clay road average gravel road 80 first class travel gravel or macadam road 55 in general the judgment should be largely the mazi mum grade by the topography of the region which the road traverses ac riling lording to the bet best current practice where the road Is or to la expected to become comerf of sufficient importance to warrant a highly improved surface the maximum grade usually la Is fixed fix edwIth with reference to this feature about as fol lows iowa per cent coastal pla plain inand and prairie 2 to a 3 average rolling country iia ii 4 to 6 hilly or mountainous regions 6 to 8 the question of minimum grado Is of importance only as regards the side ditches these should have adequate fall to empty the water that collects la in them at a sufficiently rapid rate to prevent damage to the road ordinarily it Is 19 desirable de to give the side ditches a fall of about one foot per feet of length though a somewhat loss legs fall has baa proved satisfactory some som almes wherever changes la in grade occur I 1 the change should be made by b y means of a vertical curve and not by an abrupt angle i 1 slopes the slope at which earth wili will stand I 1 when faced up in id a cut or placed in an embankment depends aon 1 on the th char chap acter of the earth and 2 on the climate inputs in cuts a good quality of non staking slaking clay usually will stand on a slope of about 45 degrees or as slope Is expressed usually one horizontal to one vertical even where fairly deep freezing occurs and in some of the southern states such material has been known to stand tor for many years on a slope of less than one half to one on the other hand clay that stakes slakes very easily may require a slope of three to one or even four to one under the most mone favorable condition of climate but this latter extreme Is 13 very unusual the usual slope for clay in cuts Is one to one in warm climates and one and one half to one la in cold climates while in the case of clay usually can be deposited on an initial slope of about one to one athla steep cari ad b bei maintained e d unless the material Is of an exceptional quality and the climate very favorable ordinarily clay embankments should have a slope of about two to one in cold climates and at least one and one half to one la in warm climates and if the clay be of questionable quality these values should b be increased embankment ban kment slopes require more care in construction than excavation sl slope oples because any flattening of an embankment slope by the action of weather after the road Is completed Is very likely to damage the road surface while the sliding in of excavation slopes usually does no further damage than to obstruct th the side ditches which can beneo be reopened bened readily sand of average quality usually requires a slope of about two to one la in cuts and three to one in embankments regardless of climate moderately course coarse sand mixed with gravel will stand on a steeper slope than fin fins sand because the former Is 16 not moved so readily by the action of storm water i solid roch rock excavation usually cabbe can be done on an average slope of about one 0 fourth to one except where the rock occurs in sloping strata separated by slippery clay seams in the latter case the average slope may be asmuth as much OB an one half to one or three fourths to one the faces of rock cuts usually are not dressed down to even an approximately smooth slope as Is conein done in earth cuts in excavating solid rock only such material Is moved as Is actually necess necessary arT to obtain the desired width at the bottom of the cut or as has been loosened in blasting the faces should of course be cleared of all material which Is loose or or which might by bg loosened subsequently by frost and slide down upon the road stone e embankments M bank ments usually will stand on a slope of about one to one in order orde r to prevent damage by washing all earth slopes in either cither excavation or should be protected by a growth of grass as soon an aa practicable after they are formed in many localities where rethe the soil is fertile and a good quality of grass la is native no seeding of the slopes Is necessary in other cases the soil may not possess sufficient fertility to grow grov grass grass even when the slopes are seed edund edana la in which evently eien event tit lt may be very cover the slopes with cut sod this latter process usually la Is very expensive and should be employed only where it Is known that thorough seed seeding fing and fertilizing would falato fall to secure a covering of sod another precaution frequently necea enry in order to prevent the washing away of excavation slopes Is to intercept water from the natural ground surface which otherwise would flow down over the excavation alope this esdone la done by me means ansof of a berta benn ditch constructed well back fr troi uthe tope the slope figure a condition which makes a beno bem d ditch tc desirable and also shows bow such fluch a ditch Is constructed |