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Show MOTORISTS NEED WIDERHIGHWAYS 18 Feet Decidedly Too Narrow Nar-row to Provide Proper Clearance. (Prepared by the United States Department ol Agriculture.) Do you know that you drive your car or truck by instinct? You do, for engineers of the bureau of public roads have been watching you. They have made observations to see how far from the edge of the. pavement you drive and what you do at curves and on down grades. Having marked off pavements Into one-foot sections, the engineers, by watching the right rear wheels of passing vehicles, find that on straight and level roads of various widths from 14 to 24 feet, with shoulders in fair condition, passenger car drivers habit ually maintain a distance of from 1 to 4 feet between the outer wheel nnd the edge of the pavement Truck drivers operate somewhat nearer the edge, but prefer not to approach closer clos-er than l'A feet. Drivers will sacrifice sacri-fice clearance between their own and passing vehicles rather than drive closer to the edge than they instinctively instinct-ively feel is safe. Pavements Too Narrow. The bureau's observations indicate that pavements less than 18 feet wide are decidedly too narrow since they provide no clearance for passenger cars or trucks operating in the usual paths. While the lS-foot width is apparently ap-parently great enough for passenger cars in two-lane traffic, it is not quite wide enough for trucks. The 20-foot width gives ample clearance for trucks and is not excessive for automobiles. In moving down hill on light" grades, traffic moves slightly toward the center cen-ter of the road. Light down grades do not suggest reduction of speed, hence traffic takes the precaution of moving slightly away from the edge of the pavement No such tendency was observed on heavy grades where the speed is reduced, and the fear of the pavement's edge is lessened. In rounding horizontal curves, traffic, traf-fic, In general, shifts toward the in-' in-' side edge, but the trucks shift courses toward the inside of the curve less than passenger vehicles. Under all circumstances, truck drivers are found to adhere more closely to the edges of the pavement than operators of passenger vehicles. Traffic Shifts Its Course. Traffic moving on the outside of the curve shifts its course farther in the direction of the Inside than traffic moving in the opposite direction, which Is limited In its choice of a course by the proximity of the edge of the pavement. Unless, therefore, the pavement Is widened on the curves, the normal straight road clearance clear-ance between the two lines of vehicles Is reduced. The used width of a pavement may frequently be considerably less than its apparent width, the observations disclosed. On straight roads, as well as on curves, the outer foot of the surfaced section Is sometimes totally Ineffective because of a bad shoulder. A c sely set guardrail, a steep crown, bad gutter, or an uneven, bumpy condition of the surface near the edge will cause the driver instinctively to seek the center of the road. In one case, a 24-foot pavement was found to have nn effective width of not more than 20 feet because of the abutments of an overhead railroad bridge which were crowded close to the edge of the pavement Smooth, white concrete shoulders at the edge of a block surface seem to lure the traffic toward the side. Center Cen-ter lines on straight roads, as well as on curves, exert a marked separatory Influence. |