the National System of Defense and Interstate Highways was created in 1956 in concept as a system of superhighways that would connect all major metropolitan areas. Much of the system as originally conceived has been completed, and much work today is devoted to maintaining and upgrading the existing system. However, as population has increased, the need for additional high-capacity routes has resulted in additions to the network. Many of these routes, such as the Interstate 69 extension and the new Interstate 73/74 corridor, are identified as high-priority corridors by Congress through the series of surface transportation acts passed during the 1990s and 2000s.
The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly called the Interstate Highway System, is a network of freeways (also called expressways) in the United States. The Interstate Highway System is a separate system within the larger National Highway System.