Transportation Conformity

Transportation conformity is required under Clean Air Act (CAA) section 176(c) (42U.S.C.7506(c)). The U.S. Environmental Protection Agency’s (EPA’s) transportation conformity rule (40 CFR 51.390 and 40 CFR 93.100- 40 CFR 93.129) establishes the criteria and procedures ensuring that federally-supported (e.g., Federal Highway Administration and Federal Transit Administration supported) highway and transit projects are consistent with (“conform to”) the state’s air quality plan (SIP).

The SIP is a blueprint detailing how regions within a state currently or with a history of not attaining a National Ambient Air Quality Standard (NAAQS) will achieve the goal of attainment or maintaining attainment. By conforming to the SIP, transportation activities should not cause or contribute to new air quality violations (i.e., degrade air quality), worsen existing violations, or delay timely attainment of the relevant NAAQS or any interim milestones.

These conformity requirements fulfill the goal of protecting public health by making sure air quality impacts are considered throughout the transportation decision-making process in areas that currently or in the past had failed to limit pollution. Conformity determinations are required for non-exempt (i.e., shown to be a regionally significant contributor to emissions) federally funded highway and transit projects before they are funded and approved for transportation plans and transportation improvement programs (see EPA's website for more information).

Transportation conformity is a process that specifically addresses emissions from on-road mobile sources (cars, trucks, buses, etc.). 40 CFR 93.118 and 40 CFR 93.124 define and describe what part of the SIP that these sources must conform to. These are defined as motor vehicle emissions budgets (MVEBs) and they differ by pollutant where the limits are for precursors (i.e., ozone involves NOx and VOC limits and PM2.5 requires direct PM2.5 itself and NOx limits). MVEBs are defined as "...the implementation plan's estimate of future [motor vehicle] emissions (40 CFR 93.124(a))" and transportation plans need to be shown to limit total emissions below these budgets (i.e., they are emissions caps).

MVEBs have been established by the Georgia EPD for the Atlanta and Macon regions for ozone. For PM2.5, MVEBs have not been established in Georgia so in the interim, there is an emissions limit of staying below 2002 emissions levels that must be abided by in the Atlanta region, Chattanooga-North Georgia, Rome-Floyd County, and Macon-Bibb County.

When SIPs and the associated MVEBs have been approved by EPA for these areas for PM2.5, transportation plans will need to conform to the new limits. However, MVEBs are goals by a given year or set of years. Therefore, the interim emissions limits (defined by less than 2002 levels) apply until the given MVEB year(s). After that, the MVEBs apply. For instance, if Macon has a MVEB set for 2020, the area has to keep emissions below the interim levels until 2020, and then abide by the 2020 MVEB going forward.

Conformity requirements apply in a region until:

a) 20 years after approval of a maintenance SIP (redesignating nonattainment area to attainment), or
b) Revocation of transportation conformity requirements by EPA for areas that attain a new, stricter NAAQS for same pollutant, or
c) Revocation of the relevant NAAQS that triggered the transportation conformity requirements.

The table below outlines the regions where transportation conformity currently applies, their SIPs, relevant pollutants, and status of budgets:

Region (MPO)

State Implementation Plan Pollutants subject to conformity MVEB approved by EPA? Budget effective year(s)
Floyd County
Redesignation Request and Maintenance Plan for the Floyd County Nonattainment Area for the 1997 PM 2.5 NAAQS1 PM2.5, NOx pending2 2023
Macon (MATS) Maintenance Plan for the Macon 8-Hour Ozone Nonattainment Area VOC, NOx
Yes 2020 (interim limits before then)
Macon (MATS) Redesignation Request and Maintenance Plan for the Macon Nonattainment Area for the 1997 PM 2.5 NAAQS1 PM2.5, NOx pending2 2023
(ARC-20 counties for PM2.5, 15 counties for ozone)3
Georgia's 15% Reasonable Further Progress State Implementation Plan Revision for the Atlanta 8-Hour Ozone Nonattainment Area VOC, NOx
Yes 2006
2008 (pending)
(ARC-20 counties for PM2.5, 15 counties for ozone)3
Redesignation Request and Maintenance Plan for the Atlanta Nonattainment Area for the 1997 8-Hour Ozone NAAQS1 VOC, NOx
Yes 2008
(ARC-20 counties for PM2.5, 15 counties for ozone)3
Redesignation Request and Maintenance Plan for the Atlanta Nonattainment Area for the 1997 PM 2.5 NAAQS1 PM2.5, NOx pending2 2024
Chattanooga-Hamilton County/North Georgia (Catoosa and Walker counties) Redesignation Request and Maintenance Plan for the Chattanooga Nonattainment Area for the 1997 PM 2.5 NAAQS1 PM2.5, NOx pending2 2025

1 Submitted to EPA, approval is pending
2 These regions have no previous MVEB for 1997 PM2.5 standard-conformity is demonstrated until the budget effective year by limiting emissions to no greater than base year (2002) emissions
3 Counties in nonattainment with 2008 ozone NAAQS are Bartow, Cherokee, Clayton, Cobb, Coweta, DeKalb, Douglas, Fayette, Forsyth, Fulton, Gwinnett, Henry, Newton, Paulding, and Rockdale with the addition of Barrow, Carroll, Hall, Spalding, and Walton for the 1997 PM2.5 NAAQS and the 1997 ozone NAAQS (conformity requirements revoked as of July 20, 2013 (77 FR 30160 (May 21, 2012))).

These regions are required to include determinations of conformity in their transportation plans and to take into account environmental impacts throughout the planning process. Below are the links to planning documents and conformity determination reports. For these areas, plans need to be updated at least every 4 years (23 USC 134 (i)(1)(B)(i)).


Atlanta Plan

Metro Atlanta Regional Council (ARC) Conformity Determination Report (CDR), Technical support documentation of CDR, ARC long range transportation plan (LRTP), ARC transportation improvement plan (TIP, short range plan), and any other plan updates.

Floyd County

Rome-Floyd County Metropolitan Planning Organization (MPO) CDR, long range transportation plan and Rome-Floyd County MPO TIP (short range plan).

Macon-Bibb County

Macon-Bibb County CDR, long range transportation plan and TIP.

Chattanooga-Hamilton County / North Georgia

CDR, long range transportation plan, TIP plus any current amendments/updates.

Accompanying and complying with the federal conformity requirements, there is the Georgia Transportation Conformity Rule ((Rules for Air Quality Control, Chapter 391-3-1-.15). A major part of ensuring transportation conformity is to have a clear layout of agency duties and responsibilities in the conformity process along with continual communications between these agencies. In compliance with this rule, the Georgia Department of Natural Resources provides a manual describing these agency roles and the interagency process.

The Download this pdf file. Georgia Department of Natural Resources Transportation Conformity Manual lists the interagency consultation, enforcement, and enforceability procedural requirements of Georgia's Transportation Conformity Rule. These requirements apply to determination of conformity of metropolitan planning organization’s plans, projects and programs to the SIP. In accordance with the requirements of Clean Air Act Section 176 (c)(4)(E), it delineates the state-specific transportation conformity processes to be followed in current and future Georgia nonattainment and maintenance areas by Metropolitan Planning Organizations, publicly-owned transit agencies, the state environmental and transportation agencies, the Executive Office of the Governor, the Federal Highway Administration, the Federal Transit Administration, and the U.S. Environmental Protection Agency.