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


Approved by the Transportation Policy Committee on March 16, 2017
Approved by the Public Policy Committee on June 4, 2017
Adopted by the Board of Direction on July 29, 2017


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 the attainment and maintenance of the National Ambient Air Quality Standards (NAAQS). 


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 conform with the State Implementation Plan (SIP) or plans for the same nonattainment area. Conformity is defined as demonstrating that a project conforms to the SIP purpose of eliminating or reducing the severity and number of violations of the NAAQS and achieving expeditious attainment of such standards. 

Transportation planning agencies must show that proposed projects, as well as Statewide Transportation Improvement Plans (STIP), that are updated on varying schedules, conform to any applicable SIP. There is currently no requirement for states with nonattainment areas to regularly update their SIP. Additionally, planning cycles for short and long-range transportation plans are not coordinated with state clean air implementation plans. This lack of coordination increases the burden on state and local officials to adjust transportation plans and to show area conformity. Otherwise the projects or plans are subject to a loss of federal funding.


The Clean Air Act, last amended in 1990, requires the Environmental Protection Agency (EPA) to establish NAAQS 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 February 2017, the air in 287 counties, with a combined population of 123.4 million, was classified as "nonattainment" for one or more of the NAAQS - primarily ozone, sulfur dioxide, and particulates. 

States containing nonattainment areas are required to develop SIPs 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. While an area's Transportation Improvement Programs (TIP) and long-range transportation plan are updated regularly, SIPs are not. The requirement to demonstrate conformity with the applicable SIP can require unnecessary revisions to these transportation plans in order to remain in conformity. Without regular and synchronized updates of SIP 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 to avoid a lapse in conformity. The potential result is reduced flexibility in meeting an area's transportation needs and in some cases, additional 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 period for updating long range transportation plans to better coordinate demonstrations of conformity without reducing air quality protection. The report also recommends modifying 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 could introduce revised standards for some criteria pollutants and possibly new criteria pollutant standards. If enacted, these revisions would affect SIPs, establishing a streamlined process for incorporating and synchronizing federal activities appropriate. The streamlined process could 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 offset future emissions, and flexibility in the timing of mitigation measures and offsets to achieve greater permanent long-term environmental benefits. Other measures that support the elimination or reduction in severity and number of violations of the 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