ates 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 engineering 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, wetland, 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 American.
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 Mr. Baker in Washington, met many of the nation’s 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