Page:America's Highways 1776–1976.djvu/388

 Wagon roads outside of cities were usually unsurfaced except for the more heavily traveled trunk routes. Highways carrying heavy tonnages of freight were surfaced with broken stone, gravel, or water-bound macadam. The National Road, for example, which was constructed westward from Cumberland, Maryland, in the early years of the 19th century, had a 20-foot surface consisting of a 12-inch bottom course and a 6-inch top course of broken stone. This was far superior to the typical highway of that period.

In addition to macadam, broken stone, and gravel, other road surface materials used with varying success were brick, asphalt, wooden planks, sand-clay and granite blocks.

The basic principles for constructing all forms of surfaces as they are known today had been discovered and put into limited practice before 1910. Except for streets in the larger metropolitan areas and major routes of commerce, most road surfaces were in a rather primitive state of improvement at that time and were to remain so for several years to come.

These roads were built for horsedrawn steel-tired traffic traveling at a top speed of 8 miles per hour. In recognition of the limited capability of animal-drawn conveyances to ascend grades, gradients seldom exceeded 5 percent, and this resulted in rather crooked locations carefully selected to avoid steep grades, closely fitted to the terrain, with small cuts and fills to save grading costs. Side slopes in both cuts and fills were as steep as the natural materials would allow, usually 1½ feet horizontal to 1 foot vertical.

In the era of animal power, 105 feet was a generous radius for horizontal curves. This would enable a four-horse team and wagon having a total length of 50 feet to round a curve without leaving a 12-foot travelled way. For two-horse rigs with wider roads, the radius could be even shorter. Vertical curves were seldom used; the vertical angle between two 5 percent grades was only about 6 degrees, and this was hardly enough of a peak or valley to cause discomfort to anyone in a vehicle traveling at 4 or 5 miles per hour.

The wagon roads were inconspicuous and, from economic necessity, “rested lightly on the land.” However, it is doubtful that their builders considered this fact as an esthetic advantage for their work or, for that matter, that they gave much thought to the appearance of the road itself. In a few eastern States, notably Massachusetts and Maryland, trees were planted along the roads, but these had a practical purpose in addition to creating visual beauty. Their shade reduced the dusting and disintegration which followed when waterbound macadam surfaces dried too rapidly.

The railroads pioneered good location methods in the early 20th century. Under the spur of competition among themselves and being relatively unhampered by manmade obstacles, the railroads began to seek locations with flatter gradients than previously accepted in the interest of greater loads and less fuel consumption. For such exacting requirements, the old method of location by which the locator went into the field, selected the route by direct observation, and set the stakes as he went along was no longer adequate in any but the most level country. The locator could be aware of only what was in the range of his vision; a better location might lie over the next hill, but he could not see it. A method had to be devised that would permit the locator to examine a wider and longer sweep of country, and to meet this need, a new method of location evolved. This is called the “topographic method” to distinguish it from the old “direct method.”

Instead of staking the centerline directly on the ground, the locator surveyed a preliminary line, or “baseline,” as a base for a strip topographic map. After completing 4 or 5 miles of topography, the locator spread his maps on a long table, and he looked down upon them as if he were an observer in a balloon. Instead of seeing only a hill in front of him he saw the country in a miniature far ahead. His vision was not obstructed by trees, and he was not annoyed by insects or the weather. He easily perceived the vital features, or “controls,” which determined the best location for the centerline that would conform with the railroad’s geometric standards.

By scaling the horizontal distances between points where his projected centerline intersected the contours of the map, the locator obtained a profile which he could analyze for gradients and earthwork balance. If this profile was unsatisfactory, he could draw another paper projection, scale a new profile, and make a new analysis. Only when he was satisfied that he had the best location did he transfer the paper projection to the ground as his final staked location for the centerline of the railroad.

It was to be many years before the art of highway location and design was to attain such a high degree of sophistication. Until about 1930, the railroad method of alinement and profile was generally considered the ultimate in design for highways as well.

Prior to and during the first decade of the 20th century, the automobile had a negligible effect on the design and construction of highways. It was looked upon as an interloper which had to adapt itself to existing streets and highways. If adjustment was necessary, it was encumbent upon the vehicle manufacturer and the operator to make such adjustment. It was considered no more inconvenient for a motorist on a rural highway to slow to 6 or 8 miles per hour for a right-angled curve than for him to do so at an urban street intersection. If climatic conditions were unfavorable for motoring, the traveler merely substituted the horse for the auto. In northern latitudes, roads were so frequently impassable for automobiles during the winter months that cars were customarily placed on jacks in the late autumn and remained there until after the spring thaws in order to preserve the tires.

Despite enactment of the 1916 Federal Aid Road Act, the harsh impact of the automobile on the highway system was felt very strongly in the second decade of the century, and this was particularly true of the roadway surface. The automobile was extremely damaging to macadam and gravel roads, which essentially were held together by the interlocking of stone 382