Federal requirements regarding transportation planning in metropolitan areas, non-metropolitan areas, and statewide settings is legally established by enabling federal legislation, or statutes. Chapter 53 of Title 49 of the U.S. Code is amended to reflect changes regarding planning requirements in legislation enacted by Congress. The federal agencies responsible for implementing these laws then write regulations, providing descriptive and procedural detail to help planning practitioners implement the new requirements effectively. Accordingly, federal regulations carry the force of federal law. Finally, advisory guidance may also exist to clarify statute and regulation. Guidance is useful for understanding the specifics and "special cases" of how federal planning law is actually implemented.
23 CFR 450 - Planning Assistance and Standards - Federal transportation planning regulations (this link goes to the highway version; the transit version, adopted by FTA at 49 CFR 613, is an identical copy that incorprates this section by reference).
23 CFR 450 - Final Rule on Statewide and Nonmetropolitan Transportation Planning and Metropolitan Transportation Planning - The FTA and FHWA joint guidance on Statewide and Nonmetropolitan Transportation Planning and Metropolitan Transportation Planning published on May 27, 2016.
FTA Circular 8100.1C - Program Guidance for Metropolitan Planning and State Planning and Research Program Grants - FTA program guidance for metropolitan planning and state planning and research program grants.
U.S. Code Title 49, Chapter 53 - Public Transportation - This is the public transportation section of U.S. Code. The Metropolitan Transportation Planning statute is found at Section 5303; Statewide Transportation Planning is found at Section 5304; and Planning Programs are found at Section 5305. The Metro and Statewide Planning sections are identical to the corresponding sections of Federal Highways code, 23 U.S.C. 134 and 135.