The Dwight D. Eisenhower National System of Interstate and Defense Highways, (commonly known as the Interstate Highway System, Interstate Freeway System or the Interstate), is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America. The system, which is named for President Dwight D. Eisenhower, who championed its formation, serves nearly all major U.S. cities. Construction was authorized by the Federal-Aid Highway Act of 1956, construction took 35 years. The network has since been extended and as of 2006 it had a total length of 46,876 miles (75,440 km). About one-third of all miles driven in the country use the Interstate system (2003 figures). The cost of construction has been estimated at $425 billion (in 2006 dollars).
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