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.
The interstate highway system was finally launched in 1956 and has been hailed as one of the greatest public works projects of the century. To build its 44,000-mile web of highways, bridges and tunnels, hundreds of unique engineering designs and solutions had to be worked out. Consider the many geographic features of the country: mountains, steep grades, wetlands, rivers, deserts, and plains. Variables included the slope of the land, the ability of the pavement to support the load, the intensity of road use, and the nature of the underlying soil. Urban areas were another problem. Innovative designs of roadways, tunnels, bridges, overpasses, and interchanges that could run through or bypass urban areas soon began to weave their way across the country, forever altering the face of America.
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