Project-Level Conformity and Hot-Spot Analyses

This page contains policy guidance, technical guidance, and other resources issued by EPA to assist agencies in completing project-level conformity analyses, including particulate matter (PM2.5 and PM10) and carbon monoxide (CO) "hot-spot" analyses.

Resources for PM Hot-Spot Analyses

• PM Hot-Spot Analyses: Guidance
• Frequently Asked Questions PM Hot-Spot Analysis
• Quantitative PM Hot-Spot Training
• PM Hot-Spot Presentations

Resources for CO Hot-Spot Analyses

• CO Hot-Spot Analyses: Guidance
• CO Hot-Spot Analyses: FHWA Categorical Finding
• Frequently Asked Questions CO Hot-Spot Analysis

Modeling Resources (PM and CO)

• Emission Models and Methods
• Air Quality (Dispersion) Models
  • Guidance on New R-LINE Additions to AERMOD 19191 for Refined Transportation Project Analyses
  • Additional Methods, Determinations, and Analyses to Modify Air Quality Data Beyond Exceptional Events
• Tools for Completing Project-level Analyses

Contact Information

Resources for PM Hot-Spot Analyses

PM Hot-Spot Analyses: Guidance

• PM Hot-Spot Guidance: Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas
  This guidance is to be used by state and local agencies to conduct quantitative PM "hot-spot analyses" for new highway and transit projects that involve significant diesel emissions. This guidance describes how to estimate project emissions using EPA's MOVES model, California's EMFAC model, AP-42, and other methods. It also outlines how to apply AERMOD for PM hot-spot analyses. The guidance includes a list of additional resources that may assist agencies in conducting quantitative PM hot-spot analyses.
  • PM Hot-Spot Guidance (pdf) (3.8 MB, October 2021, EPA-420-B-21-037)
  • PM Hot-Spot Guidance Change Bulletin: October 2021 (pdf) (182 KB, October 2021, EPA-420-B-21-038)
  • October 2026 Note: National default electric vehicle projections in MOVES5 and MOVES4 may no longer be used as part of latest planning assumptions for new transportation conformity analyses – see Sections 1.5 and 3 of the MOVES6 Policy Guidance for additional information. 
  • As of March 21, 2025, the RLINE source type within AERMOD is a regulatory option and can be used for PM hot-spot modeling. For more information, see EPA’s 2024 Appendix W Final Rule website and the latest version of the AERMOD User’s Guide found on EPA’s AERMOD website. 
     
• California: In addition to EPA’s PM Hot-Spot Guidance, including specifically Section 5, project sponsors in California should refer to the California Air Resource Board’s Project-Level Handbook for instruction on running the EPA-approved version(s) of EMFAC, for example:
  • CARB’s EMFAC2021 Project-Level Handbook (pdf) (1.5 MB, March 2021) - See the Modeling Resources (PM and CO) Emissions Models and Methods heading on this site for the latest information on using EMFAC2021 and adjustment factors for hot-spot analyses in California.
     
• Previous Guidance Change Bulletins:
  • Guidance Change Bulletin: November 2015 (pdf) (182 KB, November 2015, EPA-420-B-15-090)
  • Guidance Change Bulletin: November 2013 (pdf) (491 KB, November 2013, EPA-420-B-13-056)

Frequently Asked Questions PM Hot-Spot Analysis

• EPA FAQs 
  The following are frequently asked questions about conducting hot-spot analyses for transportation conformity purposes. EPA will update these as needed.
  • Hot-spot Analyses and Project-Level Conformity Determinations FAQs (pdf) (146 KB, August 2024, EPA-420-F-24-030)
    • These FAQs address receptor placement for PM hot-spot analyses, the use of the MOVES AVFT Tool for hot-spot analyses, and electric vehicle charging infrastructure.
    • October 2026 Note: When reading Question 2, see Section 3.7 of the MOVES6 Policy Guidance for the use of MOVES6 and previous MOVES versions for hot-spot analyses. 
    • The latest MOVES Technical Guidance found under the Emissions Models and Conformity section of EPA’s Policy and Technical Guidance for State and Local Transportation page,  includes more information about the Fuels inputs in general that may be helpful for hot-spot modeling.
  • PM Hot-Spot Analysis FAQs (pdf) (151 KB, June 2018, EPA-420-F-18-011)
    • These FAQs address questions about PM hot-spot analyses, including examples of the types of projects that would, and would not need, a PM hot-spot analysis; the geographic area that would be included in an analysis; and models and mitigation available.
  • Frequently asked questions about near roadway air pollution and health (pdf) (503 KB, August 2014, EPA-420-F-14-044)
• Federal Highway Administration PM2.5 FAQs
  FHWA has developed a series of FAQs specifically for PM2.5 project-level conformity and hot-spot analyses. These FAQs were coordinated with EPA. The FHWA PM2.5 Project-Level Conformity and Hot-Spot Analyses FAQs page has more information.

Quantitative PM Hot-spot Analysis Training

EPA's training course on implementing EPA's PM Hot-Spot Guidance is a technical, hands-on course geared toward state and local agency staff. The course focuses on using EPA’s emissions model MOVES and EPA’s dispersion model AERMOD to complete quantitative PM hot-spot analyses. The course can be self-reviewed when training sessions are not available. The PM Hot-Spot Analysis Training page provides the latest training materials and other information.

• Note, while the course is based on  earlier versions of MOVES and AERMOD, it is still largely applicable to the versions of these models currently in effect, including MOVES6. For the Fuels Input, modelers should refer to the latest version of the MOVES Hands-on Training.

PM Hot-Spot Presentations

• Transportation Conformity Hot-spot Analyses (pdf) (897.06 KB, January 16, 2020)
  This presentation, given at the January 2020 Transportation Research Board (TRB) annual conference, includes lessons learned about air quality model-to-monitor comparisons and best practices for future dispersion modeling research.

Resources for CO Hot-Spot Analyses

CO Hot-Spot Analyses: Guidance

• Using MOVES3 in Project-Level Carbon Monoxide Analyses (pdf) (911 KB, December 2021, EPA-420-B-21-047)
  This guidance describes how to use the MOVES emissions model to estimate CO emissions from transportation projects, including roadway intersections, highways, transit projects, parking lots and intermodal terminals. This guidance can be applied when using MOVES3 to complete any project-level quantitative CO analysis, including hot-spot analyses for transportation conformity determinations, completing NEPA analyses, and assessing near-road air quality.
• October 2026 Note: National default electric vehicle projections in MOVES5 and MOVES4 may no longer be used as part of latest planning assumptions for new transportation conformity analyses – see Sections 1.5 and 3 of the MOVES6 Policy Guidance for additional information. 
• The latest MOVES Technical Guidance documents can be found under the Emissions Models and Conformity section of EPA’s Policy and Technical Guidance for State and Local Transportation page.
• Guideline for Modeling Carbon Monoxide From Roadway Intersections (pdf) (1.76 MB, November 1992, EPA-454/R-92-005)
  This guidance describes how to evaluate CO air quality impacts at intersections to determine if they exceed the National Ambient Air Quality Standards for CO. This guidance still applies; please note that the MOBILE5-based emission factor sections are replaced by the “Using MOVES3 in Project-Level Carbon Monoxide Analyses” guidance above.

CO Hot-Spot Analyses: FHWA Categorical Finding

FHWA released an updated CO categorical hot-spot finding for intersection projects in January 2023 that was based on MOVES3. Any CO hot-spot analyses for conformity purposes begun after September 12, 2025, may no longer rely on the January 2023 CO categorical hot-spot finding because the finding was based on MOVES3. Any future categorical hot-spot finding will be posted on EPA and DOT’s websites.

Frequently Asked Questions CO Hot-Spot Analysis

• Hot-spot Analyses and Project-Level Conformity Determinations FAQs (pdf) (146 KB, August 2024, EPA-420-F-24-030)
  • These FAQs address receptor placement for PM hot-spot analyses, the use of the MOVES AVFT Tool for hot-spot analyses, and electric vehicle charging infrastructure. Questions 2 and 3 of this document are relevant for CO hot-spot analyses.
  • October 2026 Note: When reading Question 2, see Section 3.7 of the MOVES6 Policy Guidance for the use of MOVES6 and previous MOVES versions for hot-spot analyses. 

Modeling Resources (PM and CO)

Emissions Models and Methods

• Latest Versions of Emissions Models
  Please see the Emissions Models and Conformity section of the Policy and Technical Guidance website for the latest versions of models available for use in PM and CO hot-spot analyses.

  The following is a summary of latest on-road emissions models for quantitative PM and CO hot-spot conformity analyses. This is only a summary; refer to the appropriate guidance and model websites for more information about the applicability and use of these models. 

• MOVES Model Information and Training
  • The EPA's MOVES page provides complete information about the model, including downloads, technical guidance, and tools.
  • To receive email updates about MOVES from EPA, sign up for the MOVES listserv.
  • The MOVES training page contains information on MOVES courses and webinars, including: EPA’s Hands-on Training course geared toward state and local agency staff who will use MOVES for developing SIPs and regional conformity analyses. 
  • The PM Hot-Spot Training includes how to use MOVES at the project scale (see Module 2).

• Estimating Road Dust Emissions – PM only 
  Road or construction dust can be quantified for a PM hot-spot analysis using EPA's AP-42 method or alternative local methods. AP-42 is EPA's compilation of data and methods for estimating average emission rates from a variety of activities and sources from various sectors. EPA's website AP-42: Compilation of Air Emissions Factors has the latest version of AP-42 and more information about AP-42 in general. Emissions of re-entrained road dust from paved and unpaved roads and emissions of construction dust are addressed in AP-42, Chapter 13, "Miscellaneous Sources". The key portions of the chapter include:

  • Section 13.2: "Introduction to Fugitive Dust Sources"
  • Section 13.2.1: "Paved Roads"
  • Section 13.2.2: "Unpaved Roads"
  • Section 13.2.3: "Heavy Construction Operations" (includes road construction)

  In addition to the latest version of AP-42, alternative local methods can be used for estimating road or construction dust; in some areas, these methods may already exist and can be considered for use in quantitative PM hot-spot analyses. The method used for estimating road dust for an analysis must be evaluated and chosen through the interagency consultation process.

  Air Quality (Dispersion) Models

  General information about dispersion models (including AERMOD and CAL3QHC), meteorology preprocessors, and related tools, guidance, and outreach can be found on EPA's Support Center for Regulatory Atmospheric Modeling website.

  The SCRAM RSS feed provides updates on recent posting and additions to the SCRAM website.

  AERMOD is the required air quality model for completing PM hot-spot analyses for different types of transportation projects, including:

  • Highway and intersection projects
  • Transit, freight, and other terminal projects, and
  • Projects that involve both highway/intersections and terminals, and/or nearby sources.
  • Please refer to EPA’s web page Air Quality Dispersion Modeling - Preferred and Recommended Models for the currently approved versions of air quality (dispersion) models for quantitative PM hot-spot analyses, as recommended by EPA's "Guideline for Air Quality Models" (Appendix W to 40 CFR Part 51). ​
  • Guidance on New R-LINE Additions to AERMOD 19191 for Refined Transportation Project Analyses (pdf) (September 2019, EPA-420-B-19-042)
    Note: As of March 21, 2025, the RLINE source type within AERMOD is a regulatory option and can be used for PM hot-spot modeling. For more information, see EPA’s 2024 Appendix W Final Rule website and the latest version of the AERMOD User’s Guide found on EPA’s AERMOD website. 
  • New R-LINE Additions to AERMOD 19191 for Refined Transportation Projects (pdf) (475.64 KB, Fall 2019)
    This presentation, given via webinar in the fall of 2019, provides an overview of the above guidance (“New R-LINE Additions”).

  Exceptional Events Guidance:

  • Additional Methods, Determinations, and Analyses to Modify Air Quality Data Beyond Exceptional Events (pdf) (183 KB, April 2019, EPA-457/B-19-002)

    This guidance clarifies the types of regulatory determinations, actions, and analyses for which EPA may consider certain modified air quality monitoring data, either under the Exceptional Events Rule or under other sections of the Clean Air Act (CAA) and EPA rules or guidance.

  Tools for Completing Project-level Analyses

  • Tool to generate EMISFACT portion of an AERMOD input file
    EPA has developed a MySQL script called "MOVES2AERMOD" to automate the process of generating the EMISFACT portion of an AERMOD input file using MOVES output. The tool is intended to be used as part of a quantitative PM hot-spot analysis and can be run directly through the MOVES GUI. To obtain the tool and for more information, see the MOVES tools page.

  Contact Information

  • EPA Regional Conformity Contacts 
    EPA regional conformity staff are the primary EPA contacts for project sponsors completing project-level analyses for conformity purposes and should be contacted first for information and questions about these analyses. For the complete list of contacts by region, please see State and Local Transportation Regional Contacts.
  • Technical questions about using MOVES for project-level analyses can be directed to moves@epa.gov.
  • EPA's Office of State Air Partnerships (OSAP) maintains a list of state air quality modeling staff who have experience that may be useful to a project sponsor when completing a hot-spot analysis, including running the selected air quality model and finding representative background data for a project. See OSAP's State Contacts page for more information.