Page:America's Highways 1776–1976.djvu/390

 fragments and the cementing power of stone dust and clay. The tread patterns of pneumatic tires tended to suck the finer particles to the surface where they were caught in the turbulent air currents created by the car’s rapid movement. The result was a huge cloud of dust, stifling to the motorist and abhorrent to the property owner, but even worse was the devastating effect on the road surface. Waterbound macadam was soon reduced to a residual layer of loose coarse material filled with potholes. On roads of native clay, the surface became a dust layer 2 inches or more in depth during the dry season and as fine as powdered talc. A sudden shower would turn such a layer of dust into a thin blanket of mud as slippery as wet ice; a prolonged rain would convert it to a bottomless quagmire.

Another unexpected effect was greatly increased wear on the inside of curves and the loosening and shifting of surfacing materials from the inner to the outer side of the roadway on curves. Rather than slowing to a speed commensurate with the radius of the curve, drivers instinctively hugged the inside of the curve, even to the extent of encroaching upon the ditch slope, in order to lengthen the effective radius and to take advantage of the “banking” afforded by the ditch slope.

In the case of curves to the left, this meant crossing into the opposing lane, since the normal, high crown was customarily carried around curves. As a consequence of resistance to lateral acceleration, loose surfacing materials were thrown to the outer side of the curves, resulting in a curve of longer radius that became somewhat superelevated by traffic, rather than by design and construction.

The impact of the automobile on the early roads was not all on the negative side. In the case of gradient, for example, automobiles and trucks were capable of ascending any grade suitable for horsedrawn traffic. If the surface provided sufficient traction, grades up to 6 or 8 percent posed no serious problem for skilled operators who had mastered the art of down-shifting to a lower gear. One feature of vehicular design that was the cause of considerable consternation to many drivers ascending hills was the location of the gas tank with respect to the carburetor. Many vehicles, including the most popular make of the era, relied upon gravity flow of fuel from a tank beneath the driver’s seat to the engine’s carburetor located only 2 or 3 inches lower than the bottom of the tank. It was not uncommon to stall on a grade for lack of gas, even with a tank partly filled. There is no evidence that these experiences altered the design of highways, however.

By the year 1920, many State highway departments were recognizing the inadequacies of the design features of wagon roads, but aside from a very limited mileage of added pavement during the period 1900–1920, advances in design were very limited. It is questionable whether rural roads in many of the States up to this time were actually designed. Rather, they came into being through the gradual improvement of trails, and their shape and dimensions depended more on the skill and judgment of a maintenance man riding a split log drag than upon a professional design engineer guided by a set of design standards.

By the early 1900’s the National Road, a superior highway for its time, needed improvement. This is a section of the road near Hancock, Md., before construction.

In a report prepared by the highway commissioner of one of the States in 1915, county officials were advised:

Many of the counties. . . have the remains of roads. . . built during the early part of the nineteenth century. . . The old roads of this age still stand as monuments to the ability and farsightedness of our forefathers. . . The roads of that day were arteries of commerce. Later they gave way to the railroads and roadbuilding became a forgotten and lost science. Any man who could nap rock was a roadbuilder. With the coming of the automobile and the motor truck the road is again the artery of commerce. Interest has been revived. We are beginning to appreciate the State highways and turnpikes built nearly one hundred years ago. We find them hard to improve on, even with present day methods. We can build a better surface, but we can’t build a better subgrade. . . . . . . a road once built is rarely changed, provided it is built according to certain laws which are as old as the hills themselves. So insist that your road be properly drained, well located, taking advantage of every topographic condition. No grade should exceed a rise of 5′ in 100′, and lastly that you keep and take sufficient right of way to allow for ditches and any increase in width your road may require in the years to come. . . The right of way, roadbed and drainage openings are permanent. The surface, regardless of what it is, will sooner or later have to be replaced.

At about the same time, a neighboring State reported that 90 percent of the roads within its boundaries were earth roads and added, prophetically, that they were likely to remain earth roads for a great many years. In 1933, 18 years later, less than 14 percent of the total road mileage in that State was reported as surfaced. Despite the fact that over 13,000 miles had been paved in the interim, there had been little gain percentagewise because of expansion in the highway network. 384