根据以下材料，回答题 Highways 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. At that time， there were no national standards for size， weight restrictions， or weight of trucks. During the World War I， roads throughout the country were nearly destroyed by the weight of trucks. When General Eisenhower returned from Germany in 1919， he noted: 'The old convoy （车队） had started me thinking about good， two-lane highways， but Germany's Autobahn or motorway had made me see the wisdom of broader ribbons across the land.' The interstate highway system was finally started in 1956. To build its 44，000-mile web of highways， bridges， and tunnels， hundreds of unique engineering designs and solutions had to be worked out. Considering the many geographic features of the country such as mountains， steep grades， wetlands， rivers， deserts and plains， innovative designs of roadways began to weave their way across the country， forever altering the face of America. Today， the interstate system links every major city in the U.S.， and the U.S. with Canada and Mexico. Built with safety in mind， the highways have wide lanes and shoulders， dividing medians，or barriers， long entry and exit lanes， curves engineered for safe turns， and limited access. The death rate on highways is half that of all other U.S. roads （0.86 deaths per 100 million passenger miles compared to 1.99 deaths per 100 million on all other roads）. By opening the North American continent， highways have enabled consumer goods and services to reach people in remote and rural areas of the country， spurred the growth of suburbs，and provided people with greater options in terms of jobs， access to cultural program， health care，and other benefits. Above all， the interstate system provides individuals with what they cherish most: personal freedom of mobility. The interstate system has been an essential element of the nation's economic growth in terms of shipping and job creation: more than 75 percent of the nation's freight deliveries arrive by truck;and most products that arrive by rail or air use interstates for the last leg of the journey by vehicle. Not only has the highway system affected the American economy by providing shipping routes， it has led to the growth of spin-off industries like service stations， motels， restaurants， and shopping centers. It has allowed the relocation of manufacturing plants and other industries from urban areas to rural. National standards for paved roads were in place by 1921. 查看材料