Published: Jan 1935
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The dawn of the present century saw the beginning of a new transportation system which from that day to date has had a continuous and phenomenal growth. Mechanically propelled vehicles passing over a new type of highway comprise this system. It is true that mechanically propelled vehicles for use on highways were conceived, built and operated for several centuries prior to 1900 but at all times were in a purely experimental state. The advent of the present type of mechanically driven vehicle saw the beginning of a new type of highway, one of better design, both in location and character of materials entering into its construction. Prior to 1900, excepting in the larger cities and towns, road surfaces, as a rule, were of natural material, but with the advent of the automobile came our present extensive system of roads with varying types of more durable paved surfaces. Paved surfaces, of course, were not entirely new to this or the last century for we find that the Romans had an extensive road system, the construction of which began about 250 B. C., which included many thousands of miles of well-constructed highways with paved surfaces, with extensive masonry bridges, tunnels through the mountains and many other structures found in our more modern highways. Inquiry into this subject, however, reveals that hundreds of years before the beginning of the Christian era, the more civilized countries had paved roads, a suitable example being that at Cnosus in the Isle of Crete, which may be authentically stated as being constructed about 1500 B. C. Our present motor-vehicle transportation consists of three principal parts, the road, the vehicle, and operation. It is the road to which we propose to pay particular attention in this paper. The road must be considered in conjunction with the vehicle which travels thereon with all attending circumstances and conditions incident thereto. In a study of the motor vehicles that now use our highways we find them including high-speed passenger cars able to operate hour after hour at sustained speeds, passenger motor cars of lower speeds, passenger motor busses ranging in capacity from 16 to 40 passengers, farm trucks, motor trucks with a medium load operating at high speeds, and motor trains composed of two or more units with an axle loading of 16,000 to 20,000 lb. per axle or a total gross load ranging from 20 to 40 tons. In addition to the weights and speeds, the vehicles vary in widths from 6 ft. to 8 ft., frequently have a maximum height above the pavement of 12 ft. 6 in. and a length reaching a maximum of 60 ft. Under present practices all of these vehicles may be found operating on any one of our main highways at the same time. These motor vehicles may be called upon to render service between farms and the urban centers and between neighborhoods, between large urban centers, and for long-distance movement. For the first-named service the roads need not be of the quality of those for the latter two, in that the time element is not such an important factor and as a rule the loads are on an average much lighter since we seldom find a large motor train or motor bus operating over these secondary roads. From the foregoing it is readily seen that our road must be studied in conjunction with the vehicle and the service it is called upon to render.
Worley, John S.
Professor of Transportation Engineering, University of Michigan, Ann Arbor, Mich.