LYCOS RETRIEVER 
Interstate Highway
built 658 days ago
The highest point on the Interstate Highway System is at the Eisenhower Tunnel on Interstate 70 in the Rocky Mountains of Colorado, at the Continental Divide (elev. 11,158 feet (3401 m)). The lowest point on land is on Interstate 8 at the New River near Seeley, California (elev. -52 feet (-16 m)). The lowest point under water is on Interstate 95 in the Fort McHenry Tunnel under Baltimore Harbor in Baltimore, Maryland (elev. -107 feet (-32 m)).
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As the Interstate Highway System construction was beginning, the nation's population was about 180 million. Some 80 million vehicles traveled 800 billion miles, for the most part on two-lane roads. And the United States had its sights firmly fixed on the sky, with the creation of NASA and a national commitment to launching man into space and safely returning him home.
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Although construction on the Interstate Highway system continues, it was officially regarded as complete in 1991. The initial cost estimate for the system was $25 billion over twelve years; it ended up costing $114 billion, taking 35 years to complete. As of 2004, the system contains over 42,700 miles (68,500 km) of roads, all at least four lanes wide.
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Although construction on the Interstate Highway System continues, the removal of the last traffic signal on Interstate 90 in Wallace, Idaho, on September 15, 1991 is often cited as the completion of the system. The initial cost estimate for the system was $25 billion over 12 years; it ended up costing $114 billion (adjusted for inflation, $425 billion in 2006 dollars[9] and taking 35 years to complete.[10]
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When the Interstate Highway system was built, it was a huge undertaking. To avoid confusion with the traditional US route system, the first thing they needed to do was invent a way to keep route numbers from being confused. With the US Route highway system, numbers start in the east and north ending with the higher route numbers to the west and south. With the Interstate Highway System, they simply reversed it so that there would not be a conflict between older US routes and Interstate Highways. So, low numbered Interstate Highways are to the west and south with higher numbers in the north and east. In both cases, odd numbers travel north and south and even numbers travel east and west.
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Before the Interstate Highway System was even proposed, the United States had a basic system of two-lane highways. Today, these highways are commonly known as "US" routes, but they are in fact the original US Highway System. This system of highways was created towards the end of the 19th century, since the lack of cars hadn't created a demand for any sort of highway system before then (of course, roads had existed, but not highways).
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