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General Information for Transportation and Conformity

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Transportation conformity is required by the Clean Air Act section 176(c) (42 U.S.C. 7506(c)) to ensure that federal funding and approval are given to highway and transit projects that are consistent with ("conform to") the air quality goals established by a state air quality implementation plan (SIP). Conformity, to the purpose of the SIP, means that transportation activities will not cause new air quality violations, worsen existing violations, or delay timely attainment of the national ambient air quality standards.

To learn more about the transportation conformity program and how it is implemented, you can download a copy of the documents listed below.

  • The Bridge to Cleaner Air: Transportation Conformity (PDF) (6 pp, 3.8M, EPA-420-F-06-001, January 2006)

    This brochure provides general background on the transportation conformity process, as well as a description of benefits of the conformity program.

  • Transportation Conformity: A Basic Guide for State and Local Officials (Revised by U.S. Department of Transportation, 2017)

    This guide was originally published by U.S. DOT in 1997 and discusses the basic provisions that govern the transportation conformity process.

  • Linking Transportation and Air Quality Planning: Implementation of the Transportation Conformity Regulations in 15 Nonattainment Areas (PDF)(172 pp, 795K, EPA-420-R-99-011, March 1999) 

    This report, by researcher Arnold Howitt of Harvard's Kennedy School of Government, takes an in-depth look at transportation conformity implementation in 15 study areas from 1991 through January 1998. Using a case-study approach, the report explores the conformity rule's impact on transportation planning, air quality planning, and the relationships of the involved agencies and constituencies. The report was jointly funded by the U.S. EPA and the U.S. DOT and would be of value to conformity implementers and others who have an interest in transportation planning decisions.
    The areas in the study included: Atlanta, GA; Baltimore, MD; Boston, MA; Charolotte, NC; Chicago, IL; Denver, CO; Houston, TX; Milwaukee, WI; Northern New Jersey; New York, NY; Philadelphia, PA; Phoenix, AZ; Portland, OR; Salt Lake City, UT; and San Francisco, CA.

  • EPA-DOT Memorandum of Understanding (MOU)

    This Memorandum of Understanding (MOU) was signed by the U.S. EPA and the U.S. DOT on April 19, 2000. The purpose of the MOU is to improve coordination between the federal agencies in the transportation conformity and SIP processes. Also available, below, is a May 2, 2000, memorandum sent to the EPA Regional Offices about the MOU and a fact sheet on conformity and federal interagency coordination.

For further information or assistance regarding this Web page, contact Astrid Terry at 734-214-4812 or email:

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