The Federal-Aid Highway Act of 1956, popularly known as the National Interstate and Defense Highways Act (Public Law 84-627), was enacted on June 29, 1956, when Dwight D. Eisenhower signed the bill into law. Appropriating $25 billion for the construction of of Interstate Highways over a 20-year period, it was the largest public works project in American history to that point.

The money was handled in a highway trust fund that paid for 90 percent of highway construction costs with the states required to pay the remaining 10 percent. It was expected that the money would be generated through new taxes on fuel, automobiles, trucks and tires.

Eisenhower's support of the Federal-Aid Highway Act of 1956 can be directly attributed to his experiences in 1919 as a participant in the U.S. Army's first Transcontinental Motor Convoy across the United States on the historic Lincoln Highway, which was the first road across America. The highly publicized 1919 convoy was intended, in part, to dramatize the need for better main highways and continued federal aid. The convoy left the Ellipse south of the White House in Washington D.C. on July 7, 1919, and headed for Gettysburg, Pennsylvania. From there, it followed the Lincoln Highway to San Francisco. Bridges cracked and were rebuilt, vehicles became stuck in mud, and equipment broke, but the convoy was greeted warmly by communities across the country. The convoy reached San Francisco on September 6, 1919.

The convoy was memorable enough for a young Army officer, Lt. Col. Dwight David Eisenhower, to include a chapter about the trip, titled "Through Darkest America With Truck and Tank," in his book At Ease: Stories I Tell to Friends (Doubleday and Company, Inc., 1967). "The trip had been difficult, tiring, and fun," he said. That experience on the Lincoln Highway, plus his observations of the German autobahn network during World War II, convinced him to support construction of the Interstate System when he became President. "The old convoy had started me thinking about good, two-lane highways, but Germany had made me see the wisdom of broader ribbons across the land." His "Grand Plan" for highways, announced in 1954, led to the 1956 legislative breakthrough that created the Highway Trust Fund to accelerate construction of the Interstate System.

Eisenhower argued for the highways for the purpose of national defense. In the event of an invasion by a foreign power, the military would need good roads to be able to quickly transport troops around the country. Following completion of the highways the cross country journey that took the convoy two months in 1919 was cut down to two weeks.

Another result of the act was the direct subsidization of the suburban road infrastructure, making commutes between urban centers to suburbs much quicker, furthering the flight of citizens and businesses and divestment from inner cities, and compounding vehicle pollution and excessive petroleum use problems.

Many limited-access toll roads built prior to the act were incorporated into the Interstate system (for example, the Ohio Turnpike carries portions of Interstates 76, 80, and 90).

References

• The Greatest Decade 1956-1966 Part 1 Essential to the National Interest at United States Department of Transportation - Federal Highway Administration
• History of the Interstate Highway System at United States Department of Transportation - Federal Highway Administration
• Federal Highway Act of 1956