23 U.S.C. § 103

(a) In General .— For the purposes of this title, the Federal-aid system is the National Highway System, which includes the Interstate System. (b) National Highway System.— (1) Description .— The National Highway System consists of the highway routes and connections to transportation facilities that shall— (A) serve major population centers, international border crossings, ports, airports, public transportation facilities, and other intermodal transportation facilities and other major travel destinations; (B) meet national defense requirements; and (C) serve interstate and interregional travel and commerce. (2) Components .— The National Highway System described in paragraph (1) consists of the following: (A) The National Highway System depicted on the map submitted by the Secretary of Transportation to Congress with the report entitled “Pulling Together: The National Highway System and its Connections to Major Intermodal Terminals” and dated May 24, 1996 , and modifications approved by the Secretary before the date of enactment of the MAP–21. (B) Other urban and rural principal arterial routes, and border crossings on those routes, that were not included on the National Highway System before the date of enactment of the MAP–21. (C) Other connector highways (including toll facilities) that were not included in the National Highway System before the date of enactment of the MAP–21 but that provide motor vehicle access between arterial routes on the National Highway System and a major intermodal transportation facility. (D) A strategic highway network that— (i) consists of a network of highways that are important to the United States strategic defense policy, that provide defense access, continuity, and emergency capabilities for the movement of personnel, materials, and equipment in both peacetime and wartime, and that were not included on the National Highway System before the date of enactment of the MAP–21; (ii) may include highways on or off the Interstate System; and (iii) shall be designated by the Secretary, in consultation with appropriate Federal agencies and the States. (E) Major strategic highway network connectors that— (i) consist of highways that provide motor vehicle access between major military installations and highways that are part of the strategic highway network but were not included on the National Highway System before the date of enactment of the MAP–21; and (ii) shall be designated by the Secretary, in consultation with appropriate Federal agencies and the States. (3) Modifications to nhs .— (A) In general .— The Secretary may make any modification to the National Highway System, including any modification consisting of a connector to a major intermodal terminal or the withdrawal of a road from that system, that is proposed by a State if the Secretary determines that the modification— (i) meets the criteria established for the National Highway System under this title after the date of enactment of the MAP–21; and (ii) (I) enhances the national transportation characteristics of the National Highway System; or (II) in the case of the withdrawal of a road, is reasonable and appropriate. (B) Cooperation .— (i) In general .— In proposing a modification under this paragraph, a State shall cooperate with local and regional officials. (ii) Urbanized areas .— In an urbanized area, the local officials shall act through the metropolitan planning organization designated for the area under section 134. (c) Interstate System.— (1) Description.— (A) In general .— The Dwight D. Eisenhower National System of Interstate and Defense Highways within the United States (including the District of Columbia and Puerto Rico) consists of highways designed, located, and selected in accordance with this paragraph. (B) Design.— (i) In general .— Except as provided in clause (ii), highways on the Interstate System shall be designed in accordance with the standards of section 109(b). (ii) Exception .— Highways on the Interstate System in Alaska and Puerto Rico shall be designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway. (C) Location .— Highways on the Interstate System shall be located so as— (i) to connect by routes, as direct as practicable, the principal metropolitan areas, cities, and industrial centers; (ii) to serve the national defense; and (iii) to the maximum extent practicable, to connect at suitable border points with routes of continental importance in Canada and Mexico. (D) Selection of routes .— To the maximum extent practicable, each route of the Interstate System shall be selected by joint action of the State transportation departments of the State in which the route is located and the adjoining States, in cooperation with local and regional officials, and subject to the approval of the Secretary. (2) Maximum mileage .— The mileage of highways on the Interstate System shall not exceed 43,000 miles, exclusive of designations under paragraph (4). (3) Modifications .— The Secretary may approve or require modifications to the Interstate System in a manner consistent with the policies and procedures established under this subsection. (4) Interstate system designations.— (A) Additions .— If the Secretary determines that a highway on the National Highway System meets all standards of a highway on the Interstate System and that the highway is a logical addition or connection to the Interstate System, the Secretary may, upon the affirmative recommendation of the State or States in which the highway is located, designate the highway as a route on the Interstate System. (B) Designations as future interstate system routes.— (i) In general .— Subject to clauses (ii) through (vi), if the Secretary determines that a highway on the National Highway System would be a logical addition or connection to the Interstate System and would qualify for designation as a route on the Interstate System under subparagraph (A) if the highway met all standards of a highway on the Interstate System, the Secretary may, upon the affirmative recommendation of the State or States in which the highway is located, designate the highway as a future Interstate System route. (ii) Written agreement .— A designation under clause (i) shall be made only upon the written agreement of each State described in that clause that the highway will be constructed to meet all standards of a highway on the Interstate System by not later than the date that is 25 years after the date of the agreement. (iii) Failure to complete construction .— If a State described in clause (i) has not substantially completed the construction of a highway designated under this subparagraph by the date specified in clause (ii), the Secretary shall remove the designation of the highway as a future Interstate System route. (iv) Effect of removal .— Removal of the designation of a highway under clause (iii) shall not preclude the Secretary from designating the highway as a route on the Interstate System under subparagraph (A) or under any other provision of law providing for addition to the Interstate System. (v) Retroactive effect .— An agreement described in clause (ii) that is entered into before August 10, 2005 , shall be deemed to include the 25-year time limitation described in that clause, regardless of any earlier construction completion date in the agreement. (vi) References .— No law, rule, regulation, map, document, or other record of the United States, or of any State or political subdivision of a State, shall refer to any highway designated as a future Interstate System route under this subparagraph, and no such highway shall be signed or marked, as a highway on the Interstate System, until such time as the highway— (I) is constructed to the geometric and construction standards for the Interstate System; and (II) has been designated as a route on the Interstate System. (C) Financial responsibility .— Except as provided in this title, the designation of a highway under this paragraph shall create no additional Federal financial responsibility with respect to the highway. (5) Exemption of interstate system.— (A) In general .— Except as provided in subparagraph (B), the Interstate System shall not be considered to be a historic site under section 303 of title 49 or section 138 of this title , regardless of whether the Interstate System or portions or elements of the Interstate System are listed on, or eligible for listing on, the National Register of Historic Places. (B) Individual elements .— Subject to subparagraph (C)— (i) the Secretary shall determine, through the administrative process established for exempting the Interstate System from section 306108 of title 54 , those individual elements of the Interstate System that possess national or exceptional historic significance (such as a historic bridge or a highly significant engineering feature); and (ii) those elements shall be considered to be historic sites under section 303 of title 49 or section 138 of this title , as applicable. (C) Construction, maintenance, restoration, and rehabilitation activities .— Subparagraph (B) does not prohibit a State from carrying out construction, maintenance, preservation, restoration, or rehabilitation activities for a portion of the Interstate System referred to in subparagraph (B) upon compliance with section 303 of title 49 or section 138 of this title , as applicable, and section 306108 of title 54 .