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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Air Quality Conformity

Public transportation projects proposed for federal funding must meet the requirements of the Clean Air Act (42 USC § 85) in addition to NEPA. The purpose of the Clean Air Act is to protect and enhance air quality to promote public health and welfare of the nation. To accomplish this, the Act addresses criteria air pollutants that are regulated through the National Ambient Air Quality Standards (NAAQS). Following is a discussion which defines air quality conformity and which transportation-related pollutants are studied to determine conformity.

What is air quality conformity?
Air quality conformity is a process intended to ensure that FTA funding goes to transit activities that are consistent with the air quality goals set forth in the Clean Air Act. Air quality conformity applies to two levels of transportation activity:

  1. To metropolitan transportation plans (MTPs) and transportation improvement programs (TIPs) developed by metropolitan planning organizations (MPOs) in accordance with the FHWA-FTA planning regulation (23 CFR Part 450).
  2. To projects funded by FTA and located in areas that do not meet (nonattainment areas), or previously have not met (maintenance areas) the National Ambient Air Quality Standards (NAAQS) for a transportation-related pollutant.

The transportation-related pollutants are:

  • Ozone (O3)
  • Carbon monoxide (CO)
  • Small particulate matter (PM2.5, PM10)
  • Nitrogen dioxide (NO2)
  • and the precursors of these pollutants, which are non-methane hydrocarbon compounds (NMHC)
  • oxides of nitrogen (NO and NO2, which together are called NOx)

The conformity requirements for transportation are found in Section 176(c) of the Clean Air Act (42 USC § 7506(c)). The U.S. Environmental Protection Agency (EPA) regulation to implement the requirements is found at 40 CFR Part 93.

What is project-level conformity?
FTA must find that a transit project located in a nonattainment or maintenance area meets the project-level conformity requirements before FTA can make a grant for any element of that project’s implementation. In order to conform, a transit project must come from a currently conforming Metropolitan Transportation Plan(MTP) and Transportation Improvement Program (TIP), must not cause or contribute to any air quality hot spots, and must follow any other requirements in the State Implementation Plan (SIP)for air quality that pertain to the project.

This conformance requirement is explained in the EPA conformity regulation in 40 CFR § 93.114 and § 93.115. Under the FHWA-FTA metropolitan planning regulation, FTA only recognizes the currently conforming MTP and TIP. A project is included in the MTP if:

  1. The MTP describes the proposed improvement in sufficient detail to develop a cost estimate;
  2. In a nonattainment or maintenance area, the MTP describes the design concept and scope of the project in sufficient detail that it can be included in the regional transportation network used in the regional emissions analysis;
  3. For a New Starts or Small Starts project, the MTP includes the locally preferred alternative emerging from the Alternatives Analysis; and
  4. For a project that relates to operating, maintaining, rehabilitating, or managing the existing system, the MTP includes strategies consistent with the project.See 23 CFR § 450.322(f)(2), (3), (5), and (6).

The transit project must not cause or contribute to any air quality hotspots. This requirement is explained in the EPA conformity regulation at 40 CFR § 93.116. A hot spot is a small geographic area within the metropolitan area, such as the vicinity of a congested highway intersection, where pollutant emissions build up to a level that exceeds the NAAQS for that pollutant. A short distance from the hot spot, the pollutant concentration is much lower because the pollutant disperses as it drifts away from its source within the hot spot. This requirement applies only to projects that are located in a nonattainment or maintenance area for CO, PM2.5, or PM10. The other transportation pollutants (ozone and nitrogen dioxide) are regional in nature and do not form hot spots. For example, ozone is created by a chemical reaction of NMHC, NOx, and other precursors that is driven by energy from the sun on a hot summer day, so there is no high concentration of ozone near the source of its precursors. CO and small particulates, on the other hand, are relatively chemically inert and can build up to a high concentration near a source.

What is a carbon monoxide hot-spot analysis?
Certain transit projects located in carbon monoxide (CO) nonattainment or maintenance areas would require a quantitative CO hot-spot analysis during the environmental review process. These projects are described in 40 CFR § 93.123(a), and generally include projects that affect congested intersection (e.g. fixed guideway transit projects that take an existing traffic lane from a congested highway or projects that include major park-and-ride lots). EPA recently released a new mobile source emission factor model called MOVES (EMFAC in CA) and guidance on Using MOVES in Project-Level Carbon Monoxide Analyses. Emissions factors are modeled using the most recent version of the MOVES model (or EMFAC in CA). Then dispersion modeling approved by EPA is used to determine CO concentrations at receptor locations in the hot spot. The most commonly used, EPA-approved dispersion model for this purpose is CAL3QHC software modeling program. FHWA provides additional information on Models and Methodology for CO.

What is PM2.5 and PM10 hot-spot analysis?
Certain transit projects located in PM2.5 or PM10 nonattainment or maintenance areas would require, at present, a qualitative PM hot-spot analysis during the NEPA process. These projects are described in 40 CFR § 93.123(b) and generally include major new or expanded transit centers or stations where a large number of diesel-powered transit vehicles (diesel buses, diesel commuter rail locomotives, or diesel ferryboats) will congregate. Projects typically not of concern for PM hot spots are stations and transit centers serviced by non-diesel transit vehicles, new stations or transit centers with fewer than 10 diesel buses arriving in the peak hour, and expansion of existing stations or transit centers with an increase in arrivals during the peak hour of 10 or fewer diesel transit vehicles. FTA coordinated with FHWA and EPA in producing the guidance entitled Transportation Conformity Guidance for Qualitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas (March 2006) and its supplement that can be found on the FHWA website.

EPA released final guidance for quantitative modeling of the localized PM2.5 and PM10 impacts of certain transportation projects in December 2010. The 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. After a two-year grace period which began on December 20, 2010, the guidance is to be used by transit agencies to conduct quantitative PM hot-spot analyses for transit projects that involve significant diesel emissions. Until then, a diesel transit project requiring a PM hot-spot analysis can use the qualitative method previously described. EPA and USDOT will host training and webinars on the new PM hot-spot guidance during the two-year grace period.

What should the air quality section of my environmental document look like?
If the project is in an attainment area for all transportation-related pollutants and that area is not on the verge of falling into nonattainment, then the environmental document should state that air quality is not a concern for this project.

If the project is in a nonattainment or maintenance area for a transportation-related pollutant, then one of the purposes of the project determined during scoping may be to improve air quality. If air quality improvement is an explicit purpose of the project, then the environmental document should present, for each alternative, an estimate of the emissions reduction for each transportation-related pollutant or precursor for which the area is a nonattainment or maintenance area. The document would include in the evaluation of alternatives a comparison that shows for each alternative the change in emissions from the amount produced by the future No Build (or No Action) alternative.

If the project is in a nonattainment or maintenance area for one or more transportation-related pollutants, then the air quality section of the environmental document would also include the following:

  • Brief description of what a health-related NAAQS is
  • Indication of which of the transportation-related NAAQSs EPA has determined are exceeded, or were exceeded, in the area of the project
  • Table of the NAAQSs for the transportation-related air pollutants that are or were exceeded (An FTA environmental document may not devote any space to presenting the NAAQS for a non-transportation-related pollutant or a transportation-related pollutant for whose NAAQS the area is in attainment.)
  • Statement that, as a result of the NAAQS violation, EPA has designated the area a nonattainment or maintenance area for that pollutant, and that designation makes the project subject to the air quality conformity requirements for that pollutant
  • Indication that the project’s inclusion in the MPO’s conforming MTP is a project-level conformity requirement, and a further indication of which of the alternatives is in the MTP and where it can be found in the MTP. Same information for the TIP. The project need not be in the MTP and TIP at the time of the draft EIS or EA, but before FTA can sign a ROD, FONSI or CE determination on the preferred alternative, that alternative must be included in the conforming MTP, and the phases of the project to be advanced within the lifetime of the TIP must be in the conforming TIP.
  • Results of the hot-spot analysis for that pollutant for each of the alternatives, if the project area is a nonattainment or maintenance area for CO, PM2.5, or PM10. Normally, for CO, these results are presented in a table that gives, for each alternative, the estimated pollutant concentrations at multiple intersections or parking lots that are potential hot spots, and that compares these concentrations to those of the future No Build alternative and to the NAAQS for that pollutant.(A similar table will be appropriate for PM after December 2012, when the grace period for quantitative PM hot-spot analyses expires.)If any of the Build alternatives creates a new hot-spot violation of the NAAQS that is not also caused by the future No Build alternative, or worsens a hot-spot violation of the NAAQS caused by the future No Build, then some form of traffic mitigation to eliminate or reduce the hot spot would be needed for that alternative. In the absence of mitigation, FTA would refrain from making a conformity determination for an alternative that causes or worsens a hot spot, and that alternative would be ineligible for FTA grant assistance.
  • In the final environmental document, a commitment to the specific traffic mitigation necessary to eliminate the hot spots that would otherwise be caused by the project;
  • In the final environmental document, a list of any applicable PM2.5 and PM10 control measures in the SIP and a commitment to follow them;
  • FTA’s project-level conformity determination for the project, which is based on all of the above.

What is the Congestion Mitigation and Air Quality Improvement (CMAQ) Program?
CMAQ is a program(23 USC § 149;Clean Air Act, Section 108) designed to assist nonattainment and maintenance areas in reducing transportation emissions by developing proposals/projects to improve air quality. Examples of transit projects eligible for CMAQ funds include, but are not limited to, new transit facilities associated with new or enhanced transit service, new transit vehicles to expand a fleet or replace existing vehicles, and diesel engine retrofits. For more information, see the CMAQ Final Program Guidance (October 2008).

Additional Resources:
FHWA-FTA Metropolitan and Statewide Planning Regulation (23 CFR Part 450)

EPA’s Air Quality Conformity Regulation that applies to FTA actions (40 CFR Part 93)

FHWA’s Air Quality Conformity website

Information on Dispersion Modeling approved by EPA

EPA guidance on Using MOVES in Project-Level Carbon Monoxide Analyses

Transportation Conformity Guidance for Qualitative Hot-Spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas and its supplement

FHWA’s website for laws and regulations, policy and guidance, reference materials, research and reporting for the CMAQ program

EPA’s Final Guidance on Quantitative Modeling of PM2.5 and PM10 Hot Spots