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Policy Statement 327 - Transportation and General Conformity under the Clean Air Act

Approved by the Transportation Policy Committee on April 30, 2014

Approved by the Public Policy Committee on May 9, 2014

Adopted by the Board of Direction on July 13, 2014


The American Society of Civil Engineers (ASCE) supports an integrated and proactive approach to maintaining and improving the nation’s air quality. Clean Air Act regulations should be revised to maximize the flexibility in transportation planning to meet community needs without compromising improvements in air quality or interfering with the attainment and maintenance of the national ambient air quality standards. 


Section 176 (c) of the Clean Air Act prohibits the federal government from engaging in, supporting, providing financial assistance for, licensing, permitting, or approving any projects in areas classified as “nonattainment” under the Clean Air Act unless it can be demonstrated that those projects would conform to the State Implementation Plan (SIP) or plans for the same nonattainment area. Conformity is defined as demonstrating that a project conforms to the SIP’s purpose of eliminating or reducing the severity and number of violations of the National Ambient Air Quality Standards (NAAQS) and achieving expeditious attainment of such standards.  

Transportation planning agencies must show that proposed projects, as well as Statewide Transportation Improvement Plans (STIPs) that are updated on varying schedules, conform to any applicable SIPs. There is currently no requirement for states with nonattainment areas to regularly update their SIPs. Additionally, planning cycles for short and long range transportation plans and state clean air implementation plans are not coordinated, increasing the burden on state and local officials to adjust transportation plans and the possibility that an area will be found not in conformity, and thus subject to a cut-off of federal funding.


The Clean Air Act, last amended in 1990, requires the Environmental Protection Agency (EPA) to establish National Ambient Air Quality Standards at levels necessary to protect the public health with an adequate margin of safety based on the best available scientific data.  Despite steady improvements in air quality since the Act’s passage in 1970, as of December 2010, the air in 438 counties, with a combined population of 157.2 million, was classified as “nonattainment” for one or more of the NAAQS, primarily ozone, carbon monoxide, and particulates.  
States containing nonattainment areas are required to develop implementation plans to control air pollution from stationary sources, such as power plants, as well as mobile sources, such as automobiles, as a strategy for bringing air quality into alignment with NAAQS and continually maintaining these standards. While an area’s TIP’s and long range transportation plan are updated regularly, the requirement to demonstrate conformity with the applicable SIP can require revisions to these transportation plans in order to remain in conformity. Without the incorporation of federal activities into and the regular and synchronized update of SIPs to reflect appropriate changes in background, mobile, and stationary sources of air pollution, significant transportation improvements may require deferral, reduction in scope, or inclusion of additional offsetting improvements in order to avoid a lapse in conformity. The potential result is reduced flexibility in meeting an area’s transportation needs and in some cases, capital expenditures with minimal reduction in emissions.

A 2003 report from the General Accounting Office (Federal Planning Requirements for Transportation and Air Quality Protection Could Potentially Be More Efficient and Better Linked, GAO-03-581) specifically recommends extending the time frame for updating long range transportation plans to better coordinate demonstrations of conformity without reducing the protection of air quality and assessing a change to the Clean Air Act to include periodic updates of state air quality plans to synchronize with transportation planning.

Proposed amendments to the Clean Air Act would introduce revised standards for some criteria pollutants and possibly new criteria pollutant standards. If enacted, these revisions would affect SIPs, making a streamlined process for incorporating and synchronizing federal activities appropriate. The streamlined process can include measures such as the incorporation of a facility-wide emission budget to more efficiently accommodate minor facility-related actions, use of early emission reduction credits to emissions in advance of the conformity-driven timeframes, and flexibility in the timing of mitigation measures and offsets to achieve greater permanent long term environmental benefits by accommodating temporary periods when emissions are not fully mitigated under certain conditions. Other measures that support the elimination or reduction in severity and number of violations of NAAQS and achieving expeditious attainment of these standards while supporting state and local air quality agency objectives in a streamlined and synchronized manner are desirable.

ASCE Policy Statement 327

First Approved in 1987