23 C.F.R. § 500.103
Unless otherwise specified in this part, the definitions in 23 U.S.C. 101(a) are applicable to this part. As used in this part:
Federal-aid highways means those highways eligible for assistance under title 23, U.S.C., except those functionally classified as local or rural minor collectors.
Metropolitan planning organization (MPO) means the forum for cooperative transportation decision making for a metropolitan planning area.
National Highway System (NHS) means the system of highways designated and approved in accordance with the provisions of 23 U.S.C. 103(b) .
State means any one of the fifty States, the District of Columbia, or Puerto Rico.
Transportation management area (TMA) means an urbanized area with a population over 200,000 (as determined by the latest decennial census) or other area when TMA designation is requested by the Governor and the MPO (or affected local officials), and officially designated by the Administrators of the FHWA and the FTA. The TMA designation applies to the entire metropolitan planning area(s).
23 C.F.R. § 500.103