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. It had been lobbied for by major U.S. automobile manufacturers and championed by President Dwight D. Eisenhower, who was influenced by his experiences as a young Army officer crossing the country in the 1919 Army Convoy on the Lincoln Highway, the first road across America. Eisenhower also had gained an appreciation of the German Autobahn network as a necessary component of a national defense system while he was serving as Supreme Commander of the Allied forces in Europe during World War II. In addition to facilitating private and commercial transportation, it would provide key ground transport routes for military supplies and troop deployments in case of an emergency or foreign invasion.A stretch of I-80 in Omaha, Nebraska with a typical Interstate reassurance sign with control city listed
Initial federal planning for a nationwide highway system began in 1921, when the Bureau of Public Roads asked the Army to provide a list of roads it considered necessary for national defense. This resulted in the Pershing Map. Later that decade, highways such as the New York parkway system were built as part of local or state highway systems. As automobile traffic increased, planners saw a need for such an interconnected national system to supplement the existing, largely non-freeway, United States Numbered Highway system. By the late 1930s, planning had expanded to a system of new superhighways. In 1938, President Franklin D. Roosevelt gave BPR chief Thomas MacDonald a hand-drawn map of the U.S. marked with eight superhighway corridors for study. In 1939, BPR Division of Information chief Herbert S. Fairbank wrote a report entitled Toll Roads and Free Roads, "the first formal description of what became the interstate highway system," and in 1944 the similarly-themed Interregional Highways. The publication in 1955 of the General Location of National System of Interstate Highways, informally known as the Yellow Book, mapped out what became the Interstate System.
Although construction on the Interstate Highway System continues, I-70 through Glenwood Canyon (completed in 1992) is often cited as the completion of the originally planned system. The initial cost estimate for the system was $25 billion over 12 years; it ended up costing $114 billion (adjusted for inflation, $425 billion in 2006 dollars) and taking 35 years to complete. Additional spurs and loops/bypasses remain under construction, such as Interstate 485 in North Carolina, which has been under construction since the 1980s. A few main routes not part of the original plan remain under construction, such as Interstate 22 in Tennessee, Mississippi, and Alabama, and the extension of Interstate 69 from Indiana to Texas. Officials have also identified some non-Interstate corridors for future inclusion into the system, either by construction of new Interstate routes or upgrade of existing roads to Interstate standards.
Due to the cancellation of the Somerset Freeway, Interstate 95 is discontinuous in New Jersey. Authorized by the federal government in 2004, the Pennsylvania Turnpike/Interstate 95 Interchange Project is scheduled to connect the separate sections of I-95 to form a continuous route, completing the final section of the original plan. Construction began in 2010.
Three states have claimed the title of first Interstate Highway. Missouri claims that the first three contracts under the new program were signed in Missouri on August 2, 1956. The first contract signed was for U.S. 66. On August 13, 1956, Missouri awarded the first contract based on new Interstate Highway funding.
Kansas claims that it was the first to start paving after the act was signed. Preliminary construction had taken place before the act was signed, and paving started September 26, 1956. The state marked its portion of I-70 as the "first project in the United States completed under the provisions of the new Federal-Aid Highway Act of 1956."
According to information liaison specialist, Richard Weingroff, the Pennsylvania Turnpike could also be considered one of the first Interstate Highways. On October 1, 1940, 162 miles (261 km) of the highway now designated I-70 and I-76 opened between Irwin and Carlisle. The Commonwealth of Pennsylvania refers to the turnpike as "The Granddaddy of the Pikes".