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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.

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PM Hot-spot Analyses: 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, and other methods. It also outlines how to apply air quality models (such as AERMOD and CAL3QHCR) for PM hot-spot analyses. The guidance also includes a list of additional resources that may assist agencies in conducting quantitative PM hot-spot analyses.

    Update of November 2015: This guidance has been updated to reflect MOVES2014 and its subsequent minor revisions such as MOVES2014a, to revise design value calculations to be more consistent with other EPA programs, and to reflect guidance implementation and experience in the field. Please see the November 2015 guidance change bulletin below for more information.

    Contact: Laura Berry at berry.laura@epa.gov


    California: Project sponsors can find guidance in Section 5.2 of the PM Hot-spot Guidance for characterizing a project in terms of links. While the remainder of Section 5 and Appendices G and H no longer apply (as they reference EMFAC2011), all other sections of EPA’s PM Hot-spot Guidance are relevant. For specific guidance on using EMFAC, project sponsors in California should refer to the California Air Resource Board’s Project-Level Handbooks:

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CO Hot-spot Analyses: Guidance

  • Using MOVES2014 in Project-Level Carbon Monoxide Analyses (PDF) (55 pp, 603 K, EPA-420-B-15-028, March 2015)
    This guidance describes how to use the MOVES2014 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 MOVES2014 to complete any project-level quantitative CO analysis, including hot-spot analyses for transportation conformity determinations, modeling project-level emissions for SIP development, and completing NEPA analyses.
    Contact: Technical questions about this guidance can be directed to mobile@epa.gov.
  • Guideline for Modeling Carbon Monoxide From Roadway Intersections (PDF) (57 pp, 1.76 MB, EPA-454/R-92-005, November 1992)
    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.
  • Note: All new quantitative CO hot-spot conformity analyses outside of California must be based on MOVES2014b or MOVES2014, as the grace period for MOVES2014a. See the Federal Register notice (PDF) (5 pp, 230 K, published October 7, 2014) and EPA's latest MOVES policy guidance for details.

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CO Hot-spot Analyses: FHWA Categorical Finding

  • 2017 CO Categorical Hot-Spot Finding for Intersection Projects – Updated with MOVES2014a

    On July 17, 2017, 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. 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).

    EPA requested additional receptors in this analysis to help demonstrate that the receptors in fact do include the location of highest concentration, and thus the analysis meets the requirements of the Clean Air Act. These additional receptors are shown in the Technical Documentation, Figure 5.

    See FHWA’s CO categorical hot-spot finding website for more information about the finding.  Questions about applicability of the finding can be addressed to the appropriate EPA Regional staff or contact berry.laura@epa.gov.

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Emissions Models and Methods

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Air Quality (Dispersion) Models

  • Guidance on New R-LINE Additions to AERMOD 19191 for Refined Transportation Project Analyses (PDF) (23 pp, 749 K, EPA-420-B-19-042, September 2019)

    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.

  • Additional Methods, Determinations, and Analyses to Modify Air Quality Data Beyond Exceptional Events (PDF) (12 pp, 183 K, EPA-457/B-19-002, April 2019)

    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.

  • Recommended Air Quality (Dispersion) Models for PM Hot-spot Analyses
    The following is a summary of recommended air quality models for completing PM hot-spot analyses for different types of transportation projects. This is a reproduction of Exhibit 7-2 of the Quantitative PM Hot-spot Guidance.
Type of Project Recommended Model(s)
Highway and intersection projects AERMOD*
Transit, freight, and other terminal projects AERMOD
Projects that involve both highway/intersections and terminals, and/or nearby sources AERMOD

*Note, the grace period for the use of CAL3QHCR in PM hot-spot analyses has ended. All new PM hot-spot analyses begun after January 20, 2020 must use AERMOD. For more information, refer to EPA’s refer to EPA’s Revisions to the Guideline on Air Quality Models final rule (PDF) (54 pp, 743 K, published January 17, 2017).

  • See Section 7 of the guidance for complete information on selecting an appropriate air quality model. See below for which model versions are currently approved for regulatory use.
  • Approved Versions of Air Quality (Dispersion) Models
    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). ​

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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.

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Training and Other Resources

  • Quantitative PM Hot-spot Analysis Training
    EPA and DOT have developed a three-day training course on implementing EPA's guidance. This technical, hands-on course is geared toward state and local agencies and focuses on using emission models (including EPA's MOVES model) and air quality models (AERMOD and CAL3QHCR) for quantitative PM hot-spot analyses. The PM hot-spot analysis training page provides the latest training materials and other information.
  • MOVES Model Information and Training
    • The EPA's MOVES page provides complete information about the model, including downloads, technical guidance, and tools.
    • The MOVES listserv provides updates on MOVES and other mobile source emissions models. Sign up here.
    • EPA has developed a two-day, hands-on course geared toward state and local agencies who will use MOVES for developing SIPs and regional conformity analyses, as well as a shorter web-based course for people interested in a general overview of MOVES. The MOVES training page contains information about this and other MOVES training information, courses, and webinars.
  • Air Quality Model Information
    • More information about dispersion models (including AERMOD and CAL3QHCR), 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. Sign up here.
  • Presentations
  • Additional conformity-related training information and presentations.

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Frequently Asked Questions (FAQs)

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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.

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