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Policy and Technical Guidance for State and Local Transportation

This page contains policy guidance issued by EPA and/or the U.S. Department of Transportation to assist state and local transportation and air quality agencies implement the transportation conformity program. Policy guidance can be found on the following topics:

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Transportation Planning and Conformity Requirements

  • Baseline Year for the Baseline Year Test (in 40 CFR 93.119)
    This page provides a table showing the baseline year to be used for each NAAQS and the regulatory provision where it is found.
  • Transportation Conformity Guidance for 2008 Ozone NAAQS Nonattainment Areas (PDF) (24 pp, 180K, EPA-420-B-12-045, July 2012)
    This document provides guidance for meeting transportation conformity requirements in areas designated nonattainment for the 2008 ozone national ambient air quality standards (“2008 ozone NAAQS”). Note:  On December 23, 2014, the DC Circuit Court vacated EPA’s revocation of the 1997 ozone NAAQS for transportation conformity purposes only in NRDC v. EPA (12/23/2014).  On March 6, 2015 EPA published a final rule revoking the 1997 ozone NAAQS for all purposes.  (80 FR 12264) The final rule became effective on April 6, 2015.  This final rule also established new attainment dates for the 2008 ozone NAAQS (in accordance with the 2014 DC Circuit Court decision) based on an area’s classification. The maximum attainment dates are: marginal areas - July 20, 2015, moderate areas – July 20, 2018, serious areas – July 20, 2021, severe areas – July 20, 2027, and extreme areas – July 20, 2032.
  • Transportation Conformity Guidance for 2012 PM2.5 Nonattainment Areas (PDF) (19 pp, 193K, EPA-420-B-15-091, November 2015)
    This document provides guidance for meeting transportation conformity requirements in areas designated nonattainment for the 2012 PM2.5 national ambient air quality standards.
    • Transportation Conformity Guidance on the Revocation of the 1997 Primary Annual PM2.5 NAAQS
      This guidance describes how the revocation of the 1997 primary annual PM2.5 national ambient air quality standard (NAAQS) will be implemented and when transportation conformity stops applying for this NAAQS.  EPA committed to provide this guidance in its November 2015 guidance concerning conformity guidance for the 2012 PM2.5 NAAQS.  Questions 2.2 and 2.3 in that guidance are now outdated and no longer apply; however, the remainder of the November 2015 guidance continues to apply.
  • Guidance for Transportation Conformity Implementation in Multi-Jurisdictional Nonattainment and Maintenance Areas (PDF) (54 pp, 589K, EPA-420-B-12-046, July 2012)
    This guidance describes how transportation conformity determinations are done in areas where multiple metropolitan planning organizations (MPOs), states and/or other agencies have jurisdiction in a nonattainment or maintenance area. This guidance updates and supersedes the July 2004 “Companion Guidance for the July 1, 2004 Final Transportation Conformity Rule: Conformity Implementation in Multi-Jurisdictional Nonattainment and Maintenance Areas for Existing and New Air Quality Standards”. This guidance has been updated to apply to existing and future NAAQS, consistent with the Transportation Conformity Rule Restructuring Amendments. 
  • Updated guidance on substituting and adding transportation control measures to approved state air quality plans (PDF) (35 pp, 401K, EPA420-B-09-002, January 2009)
    This document provides updated guidance to state and local air quality and transportation agencies on implementing the Clean Air Act provision that establishes a streamlined process for substituting or adding transportation control measures to an approved state air quality plan. Transportation control measures, such as public transit and carpooling, can provide alternatives to the public that reduce motor vehicle emissions. This document supersedes the section of the February 14, 2006 interim guidance on implementing the Clean Air Act amendments made by SAFETEA-LU that addressed this provision. 
  • EPA and DOT Joint Guidance for the Use of Latest Planning Assumptions in Transportation Conformity Determinations (PDF) (23 pp, 343K, EPA420-B-08-901, December 2008)
    This guidance document supersedes the January 18, 2001 guidance memorandum to address the July 1, 2004 transportation conformity final rule revisions on the use of latest planning assumptions in transportation conformity determinations.

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Project-Level Conformity

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Emission Models and Conformity

State Implementation Plans (SIPs) and Conformity

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Quantifying Benefits of Control Measures in SIPs and Conformity

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Land Use and Conformity

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March 2, 1999 Conformity Court Decision

(subsequently incorporated into July 2004 rulemaking)

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