23 CFR 470.107 - Federal-aid highway systems.
(a) Interstate System. (1) The Dwight D. Eisenhower National System of Interstate and Defense Highways (Interstate System) shall consist of routes of highest importance to the Nation, built to the uniform geometric and construction standards of 23 U.S.C. 109(h), which connect, as directly as practicable, the principal metropolitan areas, cities, and industrial centers, including important routes into, through, and around urban areas, serve the national defense and, to the greatest extent possible, connect at suitable border points with routes of continental importance in Canada and Mexico.
(2) The portion of the Interstate System designated under 23 U.S.C. 103(c)(1)(D)(2) shall not exceed 69,230 kilometers (43,000 miles). Additional Interstate System segments are permitted under the provisions of 23 U.S.C. 103(c)(4) and section 1105(e)(5)(A) of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), Pub. L. 102-240, 105 Stat. 1914, as amended.
(b) National Highway System. (1) The National Highway System shall consist of interconnected urban and rural principal arterials and highways (including toll facilities) which serve major population centers, international border crossings, ports, airports, public transportation facilities, other intermodal transportation facilities and other major travel destinations; meet national defense requirements; and serve interstate and interregional travel. All routes on the Interstate System are a part of the National Highway System.
(2) The National Highway System shall not exceed 286,983 kilometers (178,250 miles).
(3) The National Highway System shall include the Strategic Highway Corridor Network (STRAHNET) and its highway connectors to major military installations, as designated by the Administrator in consultation with appropriate Federal agencies and the States. The STRAHNET includes highways which are important to the United States strategic defense policy and which provide defense access, continuity, and emergency capabilities for the movement of personnel, materials, and equipment in both peace time and war time.
(4) The National Highway System shall include all high priority corridors identified in section 1105(c) of the ISTEA.