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Federal Highway Administration Carbon Monoxide Categorical Hot-Spot Finding Memo

DOT Trisk Symbol Memorandum
U.S. Department of Transportation
Federal Highway Administration

Subject: INFORMATION: Federal Highway Administration Carbon Monoxide Categorical Hot-Spot Finding Memo Date: February 12, 2014
From: // Original signed by //
April Marchese
Director, Office of Natural Environment
Reply to: HEPN-10
To: Division Administrators
Federal Lands Highway Division Engineers


The purpose of this memorandum is to announce the availability of Federal Highway Administration's (FHWA's) carbon monoxide (CO) categorical hot-spot finding per the transportation conformity rule at 40 CFR 93.123(a)(3) for urban highway projects that include one or more intersections in CO maintenance1 areas, except in California. As explained in the attached CO 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. The FHWA consulted with the U.S. Environmental Protection Agency (EPA) and the Federal Transit Administration (FTA) during the development of the CO categorical hot-spot finding and addressed all issues raised by them prior to issuing the finding.


In the January 24, 2008, Transportation Conformity Rule Amendments, EPA included the provision at 40 CFR 93.123(a)(3) to allow the U.S. Department of Transportation (DOT), in consultation with EPA, to make categorical hot-spot findings in CO nonattainment and maintenance areas if appropriate modeling showed that a type of highway or transit project would not cause or contribute to a new or worsened local air quality violation of the CO national ambient air quality standards (NAAQS) or delay timely attainment of the NAAQS or required interim milestone(s), as required under 40 CFR 93.116(a). There are currently 77 CO maintenance areas across the country wherein highway project sponsors must complete a hot-spot analysis as part of their project level conformity determination (40 CFR 93.116). The FHWA expects that a large number of highway projects that include one or more intersections and are subject to the conformity hot-spot analysis requirements for CO can rely on this CO categorical hot-spot finding. This CO categorical hot-spot finding will greatly benefit all the areas outside California2 by reducing the number of hot-spot analyses that project sponsors must conduct to only those projects that cannot rely on the CO categorical hot-spot finding.

A detailed discussion of the modeling that went into developing the CO categorical hot-spot finding can be found in FHWA's CO Categorical Hot-Spot Finding Technical Document and all the model inputs and outputs used for both MOVES and CAL3QHC can be found on FHWA's CO categorical hot-spot finding website.

The preamble to the January 24, 2008, final rule (73 FR 4434) described the general process DOT would follow in order to make a categorical hot-spot finding. The process included: 1) FHWA or FTA would develop modeling, analyses and documentation to support the finding in consultation with EPA; 2) FHWA or FTA would provide EPA an opportunity to review and comment on the complete categorical hot-spot finding documentation and resolve any issues in a manner acceptable to EPA prior to issuing the finding; and 3) FHWA or FTA would make the final categorical hot-spot finding in a memorandum or letter, which would be posted on both EPA and DOT's websites. These three steps have been completed. This memorandum completes step (3), and can be found on both FHWA's CO categorical hot-spot finding website and EPA's Project-Level Conformity and Hot-Spot Analyses website.


In order to rely on the CO categorical hot-spot finding as part of their project-level conformity determination (40 CFR 93.116(a) and 93.123(a)), a project's parameters must fall within the acceptable range of modeled parameters. This means that for a project with multiple intersections, the project sponsors should follow section 4 in EPA's, “Guideline for Modeling Carbon Monoxide from Roadway Intersections” to select the highest volume and worst level of service intersections for analysis. Once the intersection(s) are identified, the project sponsor will need to look at each approach within the intersection(s) separately to compare to the acceptable ranges to rely on the CO categorical hot-spot finding.

When a particular project falls within the acceptable range to rely on the CO categorical hot-spot finding, the project sponsor would reference the finding in their project-level conformity determination, which would be subject to interagency consultation and the public involvement requirements under the National Environmental Policy Act (NEPA) and the conformity rule (40 CFR 93.105). The existing interagency consultation and public involvement processes would be used to determine if the use of the CO categorical hot-spot finding is appropriate for the project.


For questions regarding the process used to make the CO categorical hot-spot finding or how to use the finding, please contact in FHWA headquarters Emily Biondi at (202) 366-9482 or Cecilia Ho at (202) 366-9862. For questions regarding the modeling associated with the categorical hot-spot finding, please contact in the FHWA resource center Paul Heishman at (410) 962-2362 or Michael Claggett at (505) 820-2047.

1 EPA's "Greenbook" states that, "As of September 27, 2010, all carbon monoxide areas have been redesignated to maintenance areas"

2 The CO categorical hot-spot finding analysis does not apply to California which uses EMFAC for its emissions model.

Updated: 3/17/2016
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