U.S. Interstate Highway System

The largest public works project in American history/Infrastructure

The Interstate Highway System, formally known as the Dwight D. Eisenhower National System of Interstate and Defense Highways, is a network of controlled-access highways spanning approximately 78,465 kilometers across the United States. Authorized by the Federal Aid Highway Act of 1956, it was initially justified partly as a defense measure to enable rapid military transport. Construction cost roughly $500 billion in today's dollars. The longest route, Interstate 90, stretches 4,987 kilometers from Seattle to Boston. One mile in every five was originally required to be straight enough to serve as an emergency aircraft runway, though this is sometimes disputed.