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:

On this page:

• Transportation Planning and Conformity Requirements
• Project-Level Conformity
• Emission Models and Conformity
• State Implementation Plans (SIPs) and Conformity
• Quantifying Benefits of Control Measures in SIPs and Conformity
• Land Use and Conformity
• March 2, 1999 Conformity Court Decision

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 the South Coast II Court Decision (PDF) (28 pp, 480 K, November 2018, EPA-420-B-18-050)
  This document provides guidance to address how transportation conformity can be implemented in ozone nonattainment and maintenance areas affected by the February 16, 2018 decision from the U.S. Court of Appeals for the D.C. Circuit in South Coast Air Quality Management District v. EPA (“South Coast II,” 882 F.3d 1138). Specifically, this guidance describes how transportation conformity applies in areas that were nonattainment or maintenance for the 1997 ozone NAAQS (at the time that NAAQS was revoked) as well as designated attainment for the 2008 ozone NAAQS.
• Transportation Conformity Guidance for 2015 Ozone NAAQS Nonattainment Areas (PDF) (23 pp, 202 K, June 2018, EPA-420-B-18-023)
  This document provides guidance for meeting transportation conformity requirements in areas designated nonattainment for the 2015 ozone national ambient air quality standards.
• Transportation Conformity Guidance for 2008 Ozone NAAQS Nonattainment Areas (PDF) (24 pp, 180 K, 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, 193 K, 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 (PDF) (9 pp, 127 K, EPA-420-B-16-072, October 2016)
    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

• Please see Project-level hotspot for EPA’s policy and technical guidance related to project-level conformity, including:
  • Guidance for PM and CO hot-spot analyses
  • Information on approved emissions and air quality models for project-level analyses
  • Tools, training, Frequently Asked Questions (FAQs), and other project-level analysis resources
  • Contact information for project sponsors

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Emission Models and Conformity

The information here pertains to emissions models for SIP development and regional emissions analyses for transportation conformity determinations. Information on emissions models for PM and CO hot-spot conformity analyses can be found at Project-Level Conformity and Hot-Spot Analyses Emissions Models and Methods.

MOVES3 Model

• EPA’s Office of Transportation and Air Quality (OTAQ) has developed the MOtor Vehicle Emission Simulator (MOVES). See the MOVES website for further details on the model’s development and other technical supporting materials. MOVES3 is the latest version of the MOVES emissions model and is now available. Previous versions of MOVES include MOVES2010 (and minor revisions MOVES2010a and MOVES2010b) and MOVES2014 (and minor revisions MOVES2014a and MOVES2014b).
• Federal Register Notice of Availability: Official Release of MOVES3 Motor Vehicle Emissions Model for Emissions Inventories in SIPs and Transportation Conformity (PDF) (5 pp, 260 K, published January 7, 2021)
  This notice announced the use of MOVES3 for official SIP development and transportation conformity purposes in states other than California.
• Policy Guidance on the Use of MOVES3 for State Implementation Plan Development, Transportation Conformity, General Conformity, and Other Purposes (PDF) (21 pp, 455 K, November 2020, EPA-420-B-20-044)
  Guidance on how and when to use MOVES3 for SIP development, transportation conformity, general conformity, and other purposes in states other than California.
• MOVES3 Technical Guidance: Using MOVES to Prepare Emission Inventories for State Implementation Plans and Transportation Conformity (PDF) (76 pp, 1 MB, November 2020, EPA-420-B-20-052)
  Guidance on appropriate input assumptions and sources of data for the use of MOVES3 in SIP development and regional emissions analyses for transportation conformity determinations in states other than California. It also includes guidance on developing nonroad inventories with MOVES3.

MOVES2014b model

• Federal Register Notice of Availability: Official Release of MOVES2014 Motor Vehicle Emissions Model for Emissions Inventories in SIPs and Transportation Conformity (PDF) (5 pp, 230 K, published October 7, 2014)
  This notice announced the use of MOVES2014 for official SIP submissions. MOVES2014b, the latest version of MOVES2014, was not considered a major MOVES update for SIP and transportation conformity purposes.
• Policy Guidance on the Use of MOVES2014 for State Implementation Plan Development, Transportation Conformity, and Other Purposes (PDF) (18 pp, 230 K, EPA-420-B-14-008, July 2014)
  This document describes how and when to use MOVES2014 and subsequent minor revisions, including MOVES2014a and MOVES2014b, for SIP development, transportation conformity, general conformity, and other purposes.
• MOVES2014, MOVES2014a, and MOVES2014b Technical Guidance: Using MOVES to Prepare Emission Inventories for State Implementation Plans and Transportation Conformity (PDF) (73 pp, 910 K, EPA-420-B-18-039, August 2018)
  This document provides guidance on appropriate input assumptions and sources of data for the use of MOVES2014, MOVES2014a, and MOVES2014b in SIP submissions and regional emissions analyses for transportation conformity purposes.

Use of EMFAC model in California

• Federal Register Notice of Availability: Official Release of EMFAC2017 Motor Vehicle Emission Factor Model for Use in the State of California (August 15, 2019)
  This notice describes EPA's approval of the EMFAC2017 model for SIP and transportation conformity purposes in California. It also announced a two-year conformity grace period for regional emissions analyses, which ends on August 16, 2021, and a one-year conformity grace period for CO, PM10 and PM2.5 hot-spot analyses in California, which ended August 17, 2020.  (EMFAC2014 can continue to be used for regional emissions analyses until August 16, 2021; as the grace period for hot-spot analyses has ended, EMFAC2017 must be used for new hot-spot analyses in California). EPA's approval of the model does not affect MOVES model users in other states.
  Contact: Karina O'Connor at oconnor.karina@epa.gov.
• Federal Register Notice of Availability: Official Release of EMFAC2014 Motor Vehicle Emission Factor Model for Use in the State of California (December 14, 2015)
  This notice describes EPA's approval of the EMFAC2014 model for SIP and transportation conformity purposes in California. EPA's approval of the model does not affect MOVES model users in other states.
  Contact: Karina O'Connor at oconnor.karina@epa.gov.

Guidance on other models

• Federal Register Announcement of Availability: Official Release of January 2011 AP-42 Methods for Estimating Re-Entrained Road Dust from Paved Roads (PDF) (3 pp, 62K, published February 2011)
  This announcement describes EPA’s release of the January 2011 AP-42 methods for use in SIPs and transportation conformity. The January 2011 AP-42 methods must be used for new regional emissions analyses for transportation conformity determinations. This document also supersedes the portions of the August 2007 guidance memo (next item, below) that cover estimating dust from paved roads.
• Policy Guidance on the Use of the November 1, 2006, Update to AP-42 for Re-entrained Road Dust for SIP Development and Transportation Conformity (PDF) (7 pp, 110 K, EPA420-B-07-005, August 2007)
  This guidance provides details about the changes made to the AP-42 methods for road dust and how and when to use them in PM2.5 state implementation plan development and transportation conformity determinations. Note that the portions of this guidance referring to paved road dust are no longer in effect, as they have been replaced by EPA’s Federal Register announcement of February 4, 2011, found immediately above.

State Implementation Plans (SIPs) and Conformity

• Transportation Conformity Guidance for Areas Reaching the End of the Maintenance Period (PDF) (8 pp, 212K, EPA-420-B-14-093, October 2014)
  This guidance explains when transportation conformity requirements end for maintenance areas. This subject is relevant when areas approach the end of the 20 year maintenance period for certain national ambient air quality standards.
• Guidance for Developing Transportation Conformity State Implementation Plans (PDF) (31 pp, 277 K, EPA-420-B-09-001, January 2009)
  This document provides guidance on the statutory and regulatory requirements for states to develop conformity state implementation plans. This document supersedes the November 2004 Conformity SIP Guidance and Section 7 of the Interim Guidance for Implementing the Transportation Conformity Provisions in the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) (February 2006).
  • Checklist for Developing a Conformity SIP - Appendix A (PDF)(5 pp, 336 K, EPA-420-B-09-001-Appendix A, January 2009)
  • Editable Rule Model (DOC) - Appendix B(8 pp, 100 K)  Free Viewers
• Court Decision on the Phase 1 Ozone Implementation Rule 
  On June 8, 2007, the U.S. Court of Appeals for the District of Columbia Circuit responded to our petition for rehearing on the Court's December 22, 2006, decision on the Phase 1 Rule to implement the 8-hour ozone national ambient air quality standard (NAAQS). To assist Regions, Federal, State, local agencies, and Tribes, a memo was issued to the EPA regional offices on June 15, 2007. The memo summarizes the Court's opinion, and its implications for transportation conformity and the June 15, 2007, due date for submission of state implementation plans for nonattainment areas. 
• 2001 Limited Maintenance Plan for moderate PM10
  • Attachment A - Critical Design Value Estimation and Its Applications
• 1995 Limited Maintenance Plan for nonclassifiable CO Nonattainment Areas

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Quantifying Benefits of Control Measures in SIPs and Conformity

• Diesel Retrofit and Replacement Projects: Quantifying and Using Their Emission Benefits in SIPs and Conformity - Guidance for State and Local Air and Transportation Agencies (PDF) (65 pp, 1.0 MB, EPA-420-B-18-017, March 2018)
  This document provides guidance on quantifying and using emission reductions from highway and nonroad diesel vehicles, engines, and equipment that have been retrofitted or replaced with cleaner technologies. The guidance discusses how emission reductions from diesel retrofit and replacement projects can be used in a SIP and in transportation conformity and general conformity determinations, based on the new MOVES2014a methodology described in this guidance.
  • Nonroad Retrofit Tool (XLTM) (14 MB, July 2018): This spreadsheet-based tool simplifies the creation of a nonroad retrofit and replacement input table by creating a template for that table and then filling that table based on user input. Instructions are included with the tool.
• Commuter Programs: Quantifying and Using Their Emission Benefits in SIPs and Conformity – Guidance for State and Local Air and Transportation Agencies(13 pp, 498 K, EPA-420-B-14-004, February 2014 Supersedes EPA-420-B-07-015)
  This guidance describes how to credit commuter benefit programs in a SIP or transportation conformity determination. 
• Guidance for Quantifying and Using Long Duration Switch Yard Locomotive Idling Emission Reductions in State Implementation Plans (PDF) (24 pp, 399K, EPA-420-B-09-037, October 2009)
  This document provides guidance to state air pollution control agencies and the general public on how control measures to reduce switch yard locomotive idling emissions may be used to meet SIP requirements and conformity.   Update of June 2013:  The default locomotive emission factors included in this guidance have since been updated; consult www.epa.gov/otaq/locomotives.htm for the most recent emission factors. In addition, Appendix I to EPA's Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas describes how to estimate locomotive emissions at the project level and may be a useful resource when quantifying locomotive emission reductions.

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Land Use and Conformity

• Comparing Methodologies to Assess Transportation and Air Quality Impacts of Brownfields and Infill Development (PDF) (49 pp, 17K, EPA-231-R-01-001, August 2001)
  This document describes four methods for characterizing the air quality benefits resulting from infill development, compares these methodologies, and examines their advantages and disadvantages. It also includes the June 7, 2001 guidance memo listed directly below.
• Guidance on Applicable Methodologies to Account for the Benefits of Infill in SIPs and Conformity Determinations
  This memo guides the use of the four methods in preparing SIPs and transportation conformity determinations. 
• Final Policy Guidance: Improving Air Quality Through Land Use Activities. January 2001
  This document discusses how to include land use activities in a SIP. It includes examples of land use activities and discusses requirements. (See Chapter 8 for conformity requirements and examples.)
  • Announcement
  • Complete Report: Improving Air Quality Through Land Use Activities (PDF) (110 pp, 1.1M, EPA420-R-01-001, January 2001)

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March 2, 1999 Conformity Court Decision

(subsequently incorporated into July 2004 rulemaking)

• EPA's Conformity Guidance on Implementation of March 2, 1999, Conformity Court Decision (PDF) (11 pp, 46K, EPA420-F-99-025, May 1999)
  This guidance includes details about using submitted budgets in conformity, EPA's new adequacy review process, non-federal projects, SIP disapprovals, and certain safety margins consistent with the court decision. EPA released this guidance on May 14, 1999.
• U.S. DOT's Revised Guidance for the Implementation of March 2, 1999, Conformity Court Decision
  This guidance document was released on January 2, 2002, and supersedes and replaces all previous FHWA and FTA guidance implementing the Court's decision, including the supplemental guidance issued on June 18, 1999. It covers projects that can proceed during a conformity lapse.
• Revised Guidance for Implementing the March 1999 Circuit Court Decision Affecting Transportation Conformity (PDF) (4 pp, 141 K, published February 7, 2002)
  U.S. DOT's February 7, 2002 Federal Register Notice announcing their revised guidance on projects that can proceed during a conformity lapse. This notice provides DOT's rational and justification for revising the guidance.
• May 20, 2003, FHWA/FTA Guidance:  Clarification of Transportation Conformity Requirements for FHWA/FTA Projects Requiring Environmental Impact Statements 
• April 9, 2003, FTA Guidance:  Revised FTA Procedures for a conformity lapse addresses funding and approval of FTA projects during a conformity lapse.
• June 10, 1999, Federal Register Notice:  Adequacy Status of Submitted State Implementation Plans for Transportation Conformity Purposes (PDF)(3 pp, 123 K)

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