June 29, 1956 marks the signing of the National Interstate and Defense Highways Act which created the U.S. interstate highway system. To really understand the law and the reasoning behind it, it is helpful to understand the highway situation before the law was passed as well as the development of the government agencies associated with roads and highways.

Prior to the interstate highway system, there were routes crisscrossing the country; the National Archives has a map from 1926. The 20th century brought more state highways, but driving long distances was still challenging. The Good Roads Movement, begun in the latter part of the 19th century, advocated for better paved roads to connect rural areas with local cities, but the advent of the automobile made the problems that came with distance travel more acute and the need for better highways more urgent. While there was the Lincoln Highway that ran from New York to San Francisco conceived of by Carl Fisher and dedicated in 1913, generally speaking, drivers had to rely on state highways of varying quality and quantity.

The road to the national highway system of today traces its history to 1893 when the Office of Road Inquiry was founded. It was later renamed the Office of Public Roads and placed within the Department of Agriculture. The Bureau of Public Roads was created in 1915 when several smaller departments, including the Office of Public Roads, were consolidated. That is where the Bureau remained until 1939, when it became the Public Roads Administration, and was transferred to the Federal Works Agency.

It was the work of this agency and in particular, two reports to Congress, Toll Roads and Free Roads and Interregional Highways that really bolstered the case for the national highway system we have today. The Transmittal Letter that accompanied the 1939 Toll Roads and Free Road said:

The report, prepared at the request of the Congress, is the first complete assembly of data on the use being made of our national highway network. It points definitely to the corrective measures of greatest urgency and shows that existing improvements may be fully utilized in meeting ultimate highway needs.

It emphasizes the need of a special system of direct interregional highways, with all necessary connections through and around cities, designed to meet the requirements of the national defense and the needs of a growing peacetime traffic of longer range.¹

The Defense Highway Act of 1941 included money for the National Interregional Highway Committee which was authorized to review existing data and conduct surveys on the existing highway network as well as outline and recommend a limited system of national highways. This committee was chaired by Thomas H. MacDonald, then Commissioner of Public Roads—a seminal figure in the history of the interstate system. In 1944, they published Interregional Highways, and the results echoed what was contained in the 1939 report:

To incorporate within each of the several mileage limits adopted, those principal highway routes which would reach to all sections of the country, form within themselves a complete network, and jointly attract and adequately serve a greater traffic volume than any other system of equal extent and condition.²

Between the creation of the committee and the publication of the final report, the United States was busy fighting World War II. Logistics and supply activity during the war illustrated the inadequacy of the existing highway system and further showed how important logistics were for wartime and commercial activity. Additionally, the post war travel patterns of Americans illustrated that the existing system was inadequate for increasing usage for everyone. The importance of the highways meant that when the Federal Works Agency was abolished in 1949, it was important to find a new home for the Bureau of Public Roads. That is when it was transferred to the Department of Commerce.

In 1953, Dwight D. Eisenhower, who had been Supreme Commander of the Allied Expeditionary Force in Europe, became president and he had a Grand Plan to upgrade the nation's highways. Congress took up the measure and crafted a bill but passage wasn't straightforward despite broad support. A version of the bill that contained language for the Highway Trust Fund did pass and the Federal-Aid Highway Act of 1956 (also known as the National Interstate and Defense Highways Act), Public Law 84–627 (70 Stat 374) was signed. Section 108 was the National System of Interstate and Defense Highways and it said:

(a) INTERSTATE SYSTEM.—It is hereby declared to be essential to the national interest to provide for the early completion of the "National System of Interstate Highways", as authorized and designated in accordance with section 7 of the Federal-Aid Highway Act of 1944 (58 Stat. 838). It is the intent of the Congress that the Interstate System be completed as nearly as practicable over a thirteen-year period and that the entire System in all the States be brought to simultaneous completion. Because of its primary importance to the national defense, the name of such system is hereby changed to the "National System of Interstate and Defense Highways".³

Given its size, transportation has always been important for the United States. Once it became its own economic sector, streamlining regulation and coordination became even more essential. The Department of Transportation was created October 15, 1966 (Pub. L. 89-670, 80 Stat. 931) with the passage of the Department of Transportation Act. This act included the creation of the Federal Highway Administration (FHWA) from the Bureau of Public Roads and insured the story of the country's highways continued. Congress has passed a number of bills since the 1980s:

• Surface Transportation and Uniform Relocation Assistance Act in 1987 (Pub. L. 100–17, 101 Stat. 132)
• Intermodal Surface Transportation Efficiency Act of 1991 commonly shortened to ISTEA (Pub. L.102–240, 105 Stat. 1914)
• Transportation Equity Act for the 21st Century seen as TEA-21 passed in 1998 (Pub. L. 105–178, 112 Stat. 107)

The highway system was one of the biggest public works project the United States has seen and has continued to be an important activity. It has grown since the 1950s and as of 2023, the Interstate Highway System is 46,876 miles long.⁴ The nation's highways carry goods to cities and towns all over the country and Americans travel them for work and for leisure. Highways have been a large part of the story of suburban development and growth of cities and towns, and continue to be an essential part of American life and commerce.