四级复习资料大全阅读(21)_大学英语阅读

四级复习资料大全阅读(21)

　　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 44,000mile web of highways, bridge, 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, desserts, 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.

　　Long-span, segmented-concrete, cable-stayed bridges such as Hale Boggs in Louisiana and the Sunshine Skyway in Florida, and remarkable tunnels like Fort McHenry in Maryland and Mt, Baker in Washington, met many of the nations physical challenges. Traffic control systems and methods of construction developed under the interstate program soon influenced highway construction around the world, and were invaluable in improving the condition of urban streets and traffic patterns.

　　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).