Interstate Highway System

Interstate 77

Interstate Highway System, in full Dwight D. Eisenhower National System of Interstate and Defense Highways, a network of public highways established across the United States by federal law. Though highways existed in the United States before the creation of the Interstate Highway System, the passage of the Federal-Aid Highway Act of 1956 funded the construction of more than 40,000 miles (65,000 km) of roads and established guidelines for them. The responsibility for operating requirements and traffic laws rests with individual states for their sections of interstate. Interstate highways can be identified by the prefix of a letter I before the number. I-90 is the longest interstate highway, running more than 3,000 miles (4,800 km) from Seattle to Boston. By the 1990s, all 50 states had federal interstates, accounting for more than 500 million miles (805 million km) of vehicle traffic per year.