It was the 1956 Eissenhower administration legislation properly
called the Federal-Aid Highway Act which authorized the
construction of 40,000 miles of interstate highways in the US.
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The Interstate Highway System was authorized by the Federal-Aid
Highway Act of 1956 - popularly known as the National Interstate
and Defense Highways Act of 1956 - on June 29
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The Federal Highway Aid Act of 1956 and the GI Bill (also known
as the Servicemen's Readjustment Act) helped transform American
life in the 1950s.