The National Defense Highway System of U.S interstate highways was produced as an outcome of the Federal-Aid Highway Act of 1956, popularly known as the National Interstate and Defense Highways Act of 1956.

It was championed by President Dwight D. Eisenhower, and was influenced by both his experiences as a young soldier crossing the country in 1919 and by his appreciation of the German autobahn network.

Although federal commitment to build the Interstate highway system did not come until the 1950s, planning for a system of new "superhighways" began in the late 1930s. The United States already had a number of limited-access highways, such as the Pennsylvania Turnpike and the New York parkway system dating back to the 1920s (construction on the world's first limited-access highway, the Bronx River Parkway, was begun in New York State in 1907), but these were either local or state highways, and there was no interconnected national system. A need was seen for such a system to supplement the existing largely at-grade United States highway system.

Although construction on the Interstate Highway system is ongoing, it was 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.

Today the system contains over 42,700 miles of roads; see: List of Interstates

External links