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:
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) (480 KB, 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conformity applies in areas that were nonattainment or maintenance for the 1997 ozone NAAQS (at the time that NAAQS was revoked) as well as designated attainment for the 2008 ozone NAAQS.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) (201 KB, 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) (180 KB, July 2012, EPA-420-B-12-045)
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) (193 KB, November 2015, EPA-420-B-15-091)
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) (127 KB, October 2016, EPA-420-B-16-072)
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.
- Transportation Conformity Guidance on the Revocation of the 1997 Primary Annual PM2.5 NAAQS (pdf) (127 KB, October 2016, EPA-420-B-16-072)
- Guidance for Transportation Conformity Implementation in Multi-Jurisdictional Nonattainment and Maintenance Areas (pdf) (589 KB, July 2012, EPA-420-B-12-046)
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) (447 KB, January 2009, EPA420-B-09-002)
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) (365 KB, December 2008, EPA420-B-08-901)
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.
Project-Level Conformity
- Please see the Project-Level Conformity and Hot-Spot Analysis page for EPA’s policy and technical guidance related to project-level conformity, including:
- Resources for PM hot-spot analyses, including guidance, Frequently Asked Questions, training, and presentations
- Resources for CO hot-spot analyses, including guidance and FHWA's CO categorical hot-spot finding for intersection projects
- Information on approved emissions and air quality models for project-level analyses
- Contact information for project sponsors
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.
MOVES4 Model
- EPA’s Office of Transportation and Air Quality (OTAQ) has developed the MOtor Vehicle Emission Simulator (MOVES) model for estimating onroad and certain nonroad emissions. See the MOVES website for further details on the model’s development and other technical supporting materials. MOVES4 is the latest version of the MOVES emissions model and is now available.
- Federal Register Notice of Availability: Official Release of MOVES4 Motor Vehicle Emissions Model for Emissions Inventories in SIPs and Transportation Conformity (pdf) (233 KB, published September 12, 2023)
This notice announced the use of MOVES4 for official SIP development and transportation conformity purposes in states other than California. - MOVES4 Policy Guidance: Use of MOVES for State Implementation Plan Development, Transportation Conformity, General Conformity and Other Purposes (pdf) (317.3 KB, August 2023, EPA-420-B-23-009) This guidance describes how and when to use MOVES4 for SIP development, transportation conformity, general conformity, and other purposes in states other than California.
- MOVES4 Technical Guidance: Using MOVES to Prepare Emission Inventories for State Implementation Plans and Transportation Conformity (pdf) (1.3 MB, August 2023, EPA-420-B-23-011) This guidance describes appropriate input assumptions and sources of data for the use of MOVES4 in SIP development and regional emissions analyses for transportation conformity determinations in states other than California. It also includes guidance on developing nonroad inventories.
MOVES3 Model
- MOVES3 is still available for use in transportation conformity, and available for use in SIPs where state and local agencies have already completed significant work, as described in the MOVES4 Policy Guidance and Federal Register Notice above. For technical information related to MOVES3, see the MOVES Versions in Limited Current Use website.
- MOVES3 Technical Guidance: Using MOVES to Prepare Emission Inventories for State Implementation Plans and Transportation Conformity (pdf) (1.1 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.
Use of EMFAC model in California
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EPA’s approval of Heavy-Duty I/M Program Interim Adjustment Factors for EMFAC2021 and EMFAC2017 (pdf)
On May 26, 2023, EPA approved interim off-model adjustment factors for use in California that account for the emission benefits of California’s Heavy-Duty Vehicle Inspection and Maintenance Program for use in transportation conformity determinations in California. These adjustment factors are multipliers that would be applied to vehicle emissions modeled by EMFAC2021 or EMFAC2017.The HD I/M adjustment factors for EMFAC2021 and EMFAC2017 are approved for regional emissions analyses in transportation plan and TIP conformity determinations where the SIP motor vehicle budgets are based on EMFAC2021 or EMFAC2017. These adjustment factors are not approved for CO, PM10, or PM2.5 hot-spot analysis for project-level conformity determinations. The EMFAC2017 adjustment factors also account for benefits of additional regulations included in EMFAC2021, similar to the adjustment factors approved with EMFAC2021 (more information below). Therefore, MPOs should apply only one set of EMFAC2017 adjustment factors. In addition, the EMFAC2017 adjustment factors can no longer be used for new regional emissions analyses after the end of the EMFAC2021 transportation conformity grace period.
The California Air Resources Board (CARB) requested EPA’s approval of these adjustment factors in the following letters:- CARB letter of April 10, 2023 (pdf)
- CARB letter of February 17, 2023 (pdf)
- For adjustment factors, see CARB’s EMFAC Software and Technical Support Documentation website.
- Federal Register Notice of Availability: Official Release of EMFAC2021 Motor Vehicle Emission Factor Model for Use in the State of California (published November 15, 2022)
This notice describes EPA's approval of the EMFAC2021 model for SIP and transportation conformity purposes in California. It also announces a two-year conformity grace period for regional emissions analyses, which ends on November 15, 2024, and a one-year conformity grace period for CO, PM10 and PM2.5 hot-spot analyses in California, which ends November 15, 2023. Once the grace periods end, EMFAC2021 must be used for new regional emissions analyses and hot-spot analyses in California. EPA's approval of the model does not affect MOVES model users in other states.This notice also describes EPA’s approval of the EMFAC2017 Off-Model Adjustment Factors for use in California SIP development and in regional conformity emissions analyses where adequate SIP motor vehicle emissions budgets are based on EMFAC2017 with adjustment factors. EMFAC2017 adjustment factors are not approved for CO, PM10, or PM2.5 hot-spot analyses for transportation conformity. The California Air Resources Board (CARB) requested EPA’s approval of the EMFAC2021 model as well as approval of adjustment factors to their previous model, EMFAC2017, in the following letters:
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) (154 KB, 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) (110 KB, August 2007, EPA420-B-07-005)
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) (196 KB, October 2014, EPA-420-B-14-093)
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) (336 KB, January 2009, EPA-420-B-09-001)
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) (336 KB, January 2009, EPA-420-B-09-001-Appendix A)
- Editable Rule Model - Appendix B (doc)
- 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, 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. - Guidance on the Limited Maintenance Plan Option for Moderate PM2.5 Nonattainment Areas and PM2.5 Maintenance Areas (pdf) (2.6 MB, October 2022, EPA-420-B-22-044)
This document clarifies the EPA’s Limited Maintenance Plan (LMP) guidance for PM2.5 maintenance plan submissions by state, local, and tribal air agencies, and it provides information on transportation conformity and general conformity in areas that are considering development of a PM2.5 LMP. This guidance applies for any existing PM2.5 National Ambient Air Quality Standard (NAAQS) and for any future PM2.5 NAAQS. This PM2.5 LMP Guidance applies the 2001 Limited Maintenance Plan Option for Moderate PM10 Nonattainment Areas guidance for PM2.5 LMP submissions, except for specific topics it addresses where the 2001 guidance is superseded. - 2001 Limited Maintenance Plan Option for Moderate PM10 Nonattainment Areas
- 1995 Limited Maintenance Plan Option for Nonclassifiable CO Nonattainment Areas
Quantifying Benefits of Control Measures in SIPs and Conformity
- Guidance on Quantifying NOx Benefits for Cetane Improvement Programs for Use in SIPs and Transportation Conformity (pdf) (470 KB, February 2023, EPA-420-B-23-006)
This document provides guidance on how to quantify emission reductions from state cetane improvement programs. This guidance updates and supersedes the 2004 Guidance on these programs.
Note: While much of the information in the 2004 Guidance remains relevant, updates are needed to account for changes in fleet composition and control technology that have occurred since 2004, which have greatly reduced the emissions reductions attributable to these types of programs. The 2023 document also provides updated information on the CAA’s fuel preemption provisions, which have changed since the 2004 Guidance was released. - 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) (1.0 MB, March 2018, EPA-420-B-18-017)
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.- Note: This MOVES2014-based guidance continues to be relevant for the latest version of the MOVES model: both onroad and nonroad MOVES instructions in this guidance continue to apply. This document refers to the MOVES Technical Guidance; please refer to the latest version at the Emission Models and Conformity heading above.
- 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 (pdf) (498 KB, 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) (308 KB, October 2009, EPA-420-B-09-037)
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 Regulations for Emissions from Locomotives 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.
Land Use and Conformity
- Comparing Methodologies to Assess Transportation and Air Quality Impacts of Brownfields and Infill Development (pdf) (1.6 MB, August 2001, EPA-231-R-01-001)
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) (1.2 MB, January 2001, EPA420-R-01-001)
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) (532 KB, May 1999, EPA420-F-99-025)
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) (141 KB, 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 rationale 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) (123 KB, published June 10, 1999)