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Transportation Conformity: A Basic Guide for State and 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 below 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

Chart showing two parts of Conformity. Air Quality Planning, State Implementation Plan (SIP) and Transportation Planning, Metropolitan Transportation Plan and Transportation Improvement Program (TIP).

3 Title 23 and Title 49 of the United States Code (U.S.C.) codify the transportation laws including the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, SAFETEA-LU. These include transportation planning provisions that govern the programs of the Federal Highway Administration (FHWA) and the Federal Transit Administration (FTA).

4 The transportation conformity rule, as amended, is available at conformity/

Updated: 3/14/2012
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