Page:America's Highways 1776–1976.djvu/391

 The same section of road after construction.

Nationwide, the mileage of high type pavements on rural highways in 1920 was negligible in relation to the total miles of highway, although substantial gains had been made in gravel surfacing up to that time. Regretably, however, much of the rural pavement in place at the beginning of World War I was destroyed by heavy trucking in pursuance of the war effort.

The period 1920–1930 may be characterized as a period of trial and error in adapting an assortment of roads laid out for use by horses and wagons to the use of automobiles and trucks. While the highway system continued to expand during this period, particularly in the agricultural belt of the Plains States, the nature of the added highways was generally the same as the earlier wagon roads with perhaps the addition of an all-weather surface, frequently gravel or sand-clay. Except for roads in the New England and North Atlantic States and in portions of the Pacific States, few rural roads in 1920 were surfaced with anything better than sand-clay or gravel. If one were careful in selecting his route, he could travel from New York City to Washington, D.C., on paved highways. From Washington to Richmond, however, the best route was one-third longer than the most direct one and included 99 miles of gravel surface rather than a paved surface. From Chicago to Milwaukee, according to a prominent guidebook of the day, the entire 92 miles was paved with concrete or macadam “except for one very rough mile.” Going south from Chicago, the route to Lafayette, Indiana, consisted of 98 miles of gravel, 26 miles of macadam, and 16 miles of dirt. The entire 102-mile route from Atlanta to Macon, Georgia, consisted of sand-clay roads. With these segments of interstate highways in the conditions described, it requires little imagination to visualize the condition of the lesser important routes. Clearly, the most pressing need was for all-weather surfacing, and this was the course that the roadbuilding program followed.

While most highway authorities were conscious of a need to modify the highway cross section and alinement to meet the requirements of motorized traffic, there was little precedent upon which to base judgments of immediate design requirements, or worse, for predicting those of the future. Highway engineers had much in common with one self-made automotive engineer of this period who has been quoted to the effect that, “If itsit’s [sic] in a book itsit’s [sic] out of date.”

Elements recognized as warranting special consideration because of higher vehicular speed included sight distance, curvature, and superelevation. Variables taken into account because of the volume and character of traffic were pavement width and structural needs. The manner of satisfying these requirements varied not only between States, but within States. Minnesota, for example, found that, “Abrupt narrow curves have contributed their share to fatal accidents. . . which it is expected will be relieved by. . . [a] requirement for a clear sight distance of 200 feet on all State roads with widening and banking on curves.” In 1921 it was the practice in Illinois, as another example, to eliminate right-angled turns “whenever possible,” and where such turns were necessary, a minimum radius of 500 feet was used. Moreover, “All curves which have a radius of less than 6,000 feet are super-elevated. . .” The speed upon which the superelevation was based was the legal speed limit which, in 1921, was 25 m.p.h. This was increased to 35 m.p.h. in 1928, with a maximum superelevation of 1 inch per foot for curves with radii of less than 1,000 feet. The State of California, among others, had earlier considered the matter of superelevation and, in 1917, had reached a compromise decision to apply superelevation to concrete pavements on mountain roads only. The rate of superelevation to be applied varied from a maximum of ¾ inch per foot for curves having a radius of 75 feet or less to ⅛ inch per foot for radii within the range of 225 to 300 feet. A few States used spiral transitions, but the practice was not widespread. Obviously, most decisions in the matter of roadway geometry were arbitrarily made and had little scientific support.

Perhaps the element that varied most widely was the width of surfacing. In Kentucky, for example, during the years just before and after 1920, contracts were awarded for pavements ranging from 9 to 20 feet in width, with 14 feet predominating. Most bridges had either 12- or 16-foot roadways. In Illinois during the same period, concrete and brick pavements were 10, 15, and 18 feet wide. It was common practice at about this time to construct pavements with sufficient width to accommodate only a single lane of traffic. There was some disagreement as to whether the best position for such a pavement was in the center of the roadbed or at the right-hand side 385