History of the Automobile and National Highway System

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In the numbering scheme, east–west highways are assigned even numbers AND the south–north highways are assigned odd numbers.

Requires the Federal Highway Administration to ensure that the State transportation departments maintain "effective control of the erection and maintenance" of signs, displays, or devices, including outdoor advertising signs that are visible from the highway, beyond 660 feet of the Interstate right-of-way outside urban areas, and erected with the purpose of their message being read from the highway.

The American Association of State Highway and Transportation Officials (AASHTO) present numbering policy dates back to August 10, 1973. Within the continental United States, primary Interstates – also called main line Interstates or two-digit Interstates – are assigned numbers less than 100.

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The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly called the Interstate Highway System (or simply the Interstate), is a network of limited-access highways (also called freeways or expressways) in the United States.

Note: *The Interstate Highway System (IHS) is a subsystem of the National Highway System.