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

Resources for CO Hot-Spot Analyses

Modeling Resources (PM and CO)

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
    EPA has released final guidance for modeling the local air quality impacts of certain transportation projects on the PM2.5 and PM10 national ambient air quality standards (NAAQS). 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.

    September 2023 Note: The October 2021 version of this guidance based on MOVES3 generally continues to apply for MOVES4, with the exception of new guidance for the AVFT fuels input found in the 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) . Please refer to Section 4.8.3 of the MOVES4 Technical Guidance for this input. Section 4.8 of the MOVES4 Technical Guidance includes more information about the Fuels inputs in general that may be helpful for PM hot-spot modeling.

    Update of October 2021: This guidance update includes new guidance on the number of MOVES runs, reflects that AERMOD is the required model for PM hot-spot analyses, and reflects guidance implementation and experience in the field. EPA also clarifies that the technical information in this guidance may also apply when completing analyses of transportation projects for other purposes, such as general conformity, National Environmental Policy Act (NEPA) analyses, or assessing near-source air quality in communities with environmental justice concerns. Sources could include roads, freight terminals, and railyards. Please see the October 2021 guidance change bulletin below for more information.


    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:

  • Previous Guidance Change Bulletins:

Frequently Asked Questions (FAQs)

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 MOVES2014a, it is still largely applicable to MOVES3.

PM Hot-Spot Presentations

  • Transportation Conformity Hot-Spot Analyses
    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.
  • PM Hot-Spot Modeling: Lessons Learned in the Field
    This presentation, given at the January 2014 TRB annual conference, covers some of the modeling issues that have arisen in the field and the correct application of the models for hot-spot modeling.
  • Overview of EPA's Quantitative PM Hot-Spot Guidance
    This general overview was presented several times after the release of the guidance in 2011 and was updated October 2014. Note that CAL3QHCR can no longer be used for transportation conformity hot-spot analyses.

Resources for CO Hot-Spot Analyses

CO Hot-Spot Analyses: Guidance

  • Using MOVES3 in Project-Level Carbon Monoxide Analyses (pdf) (December 2021, EPA-420-B-21-047)
    This guidance describes how to use the MOVES3 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 in communities with environmental justice concerns.

    September 2023 Note: The December 2021 version of this guidance based on MOVES3 generally continues to apply for MOVES4, with the exception of new guidance for the AVFT fuels input found in the . Please refer to Section 4.8.3 of the MOVES4 Technical Guidance for this input. Section 4.8 of the MOVES4 Technical Guidance includes more information about the Fuels inputs in general that may be helpful for CO hot-spot modeling.

  • 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

  • 2023 CO Categorical Hot-Spot Finding for Intersection Projects – (MOVES3)

    September 2023 Note: This CO categorical hot-spot finding can continue to be relied upon for the duration of the MOVES4 conformity grace period, i.e., through September 12, 2025. See Question 15 of the for more information.

    On January 31, 2023, the Federal Highway Administration (FHWA) announced the availability of an updated carbon monoxide categorical hot-spot finding for certain projects involving a large urban intersection. This finding supersedes FHWA’s 2017 CO Categorical Hot-Spot Finding that was completed with MOVES2014a.

    Where a project’s parameters fit the conditions of the categorical hot-spot finding, project sponsors may be able to rely on the categorical hot-spot finding in place of doing their own CO hot-spot analysis as part of a project-level conformity determination in CO maintenance areas outside of California. The interagency consultation process should be used to determine whether the CO categorical hot-spot finding applies to a particular project, and any project-level conformity determination that relies on FHWA’s finding would be subject to public involvement requirements (40 CFR 93.105).

    FHWA’s 2023 categorical finding is based on an intersection and includes four scenarios based on high and low percentages of trucks and high and low road grades. In addition, the acceptable ranges for other parameters (intersection angle, speed, lane width, etc.) have been expanded.

    See FHWA’s CO Categorical Hot-Spot Finding website for more information about the finding, including a spreadsheet tool that can be used to assess and document whether the analysis applies to a specific project. Questions about applicability of the finding can be addressed to the appropriate EPA Regional staff.

Frequently Asked Questions (FAQs)

Modeling Resources (PM and CO)

Emissions Models and Methods

  • Latest Versions of Emissions Models
    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.
     
    Emissions Model Geographic Applicability Federal Register Notice Link to Model Information
    MOVES4 All states other than California Official Release of MOVES4 Motor Vehicle Emissions Model for Emissions Inventories in SIPs and Transportation Conformity (pdf) (233 KB, published September 12, 2023)

    Latest Version of MOtor Vehicle Emission Simulator (MOVES)

    See Emission models and conformity for the MOVES4 Policy Guidance.
    MOVES3 All states other than California Official Release of MOVES3 Motor Vehicle Emissions Model for Emissions Inventories in SIPs and Transportation Conformity (PDF) (published January 7, 2021)

    MOVES Versions in Limited Current Use
    EMFAC2021 California only Official Release of EMFAC2021 Motor Vehicle Emissions Factor Model for Use in the State of California (November 15, 2022) MSEI - Modeling Tools - EMFAC Software and Technical Support Documentation
  • 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 MOVES courses and webinars, including: EPA’s two-day, hands-on course geared toward state and local agency staff who will use MOVES for developing SIPs and regional conformity analyses. The course can be self-reviewed when training sessions are not available.
    • 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. The sections of AP-42 that address emissions of re-entrained road dust from paved and unpaved roads and emissions of construction dust are found 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 (SCRAM) 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)
      This guidance addresses the use of the new R-LINE features in AERMOD 19191 for dispersion modeling of transportation sources. The guidance also explains that some of these features can be used for transportation conformity purposes only with EPA approval and some of these features cannot be used for regulatory purposes at this time.
    • New R-LINE Additions to AERMOD 19191 for Refined Transportation Projects
      This presentation, given via webinar in the fall of 2019, provides an overview of the above guidance (“New R-LINE Additions”). It focuses on the R-LINE features of AERMOD 19191 and the circumstances under which they can be used.

    Exceptional Events 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 mobile@epa.gov.
    • EPA's Office of Air Quality Planning and Standards 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 OAQPS's State Contacts page for more information.

State and Local Transportation

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Last updated on August 22, 2024