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Transportation Conformity: A Basic Guide for State & Local Officials


The air quality provisions of the Clean Air Act (CAA) and the metropolitan transportation planning provisions of Title 23 and Title 49 of the United States Code3 require a planning process that integrates air quality and metropolitan transportation planning such that transportation investments support clean air goals. This process is known as transportation conformity and is carried out in accordance with 40 CFR Parts 51 and 934. Exhibit 1 illustrates how conformity plays a central role as the link between transportation and air quality planning.

Exhibit 1: Conformity Links Air Quality and Transportation Planning

Conformity links air quality planning and transportation planning. Text: This graphic shows the two primary components of conformity. The first is air quality planning, primarily the State implementation plan. The second component shown is Transportation Planning, which includes the Metropolitan Transportation Plan and the Transportation Improvement Program.

3Title 23 and Title 49 of the United States Code (U.S.C.) codify the transportation laws including the Fixing America's Surface Transportation Act (FAST Act). These include transportation planning provisions that govern the programs of the FHWA and the FTA.

4The transportation conformity rule is available at

Updated: 4/11/2017
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