Early in the 20th century, most of the streets and roads in the U.S. were made of dirt, brick, and cedar wood blocks. Built for horse, carriage, and foot traffic, they were usually poorly cared for and too narrow to accommodate(容纳)automobiles.
With the increase in auto production, private turnpike(收费公路)companies under local authorities began to spring up, and by 1921 there were 387,000 miles of paved roads. Many were built using specifications of 19th century Scottish engineers Thomas Telford and John Mac Adam (for whom the macadam surface is name [D], whose specifications stressed the importance of adequate drainage. Beyond that, there were no national standards for size, weight restrictions, or commercial signs. During World War I, roads throughout the country were nearly destroyed by the weight of trucks. When General Eisenhower returned from Germany in 1919, after serving in the U.S. Armys first transcontinental motor convoy (车队), he noted: The old convoy had started me thinking about good, two-lane highways, but Germanys Autobahn or motorway had made me see the wisdom of broader ribbons across the land.
It would take another war before the federal government would act on a national highway system. During World War II, a tremendous increase in trucks and new roads were required. The war demonstrated how critical highways were to the defense effort. Thirteen per cent of defense plants received all their supplies by truck, and almost all other plants shipped more than half of their products by vehicle. The war also revealed that local control of highways had led to a confusing variety of design standards. Even federal and state highways did not follow basic standards. Some states allowed trucks up to 36,000 pounds, while others restricted anything over 7,000 pounds. A government study recommended a national highway system of 33,920 miles, and Congress soon passed the Federal-Aid Highway Act of 1944, which called for strict, centrally controlled design criteria.
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