CONCURRENT AIR QUALITY ANALYSIS UNDER
THE NATIONAL ENVIRONMENTAL POLICY ACT AND TRANSPORTATION/AIR
Randall Guensler, Ph.D.
The Conformity Rule, adopted in November 1993 by the U.S. Environmental Protection Agency under
the requirements of Section 176 of the Clean Air Act, establishes strict procedures for determining the
conformity of transportation plans and state air quality management plans.
apply to all transportation plans, programs, and projects, funded or approved under title 23 (Highways)
U.S.C. or the Federal Transit Act.
Under Conformity, transportation planning agencies must apply
transportation activity and vehicle emission rate models to demonstrate that transportation plans,
programs, and projects will not exceed allowable emissions budgets established in the air quality
Furthermore, transportation planning agencies must apply microscale air quality
impact models to demonstrate that projects will not cause a violation of local air quality standards.
This paper addresses the direct and indirect relationships between the National Environmental Policy
Act (NEPA) and the new conformity requirements.
This paper concludes that NEPA and
transportation/air quality conformity processes should be concurrent.
The need for concurrent
determinations is supported by five arguments:
1) the legislative history of conformity indicates that
project conformity determinations be made during the NEPA process;
2) general NEPA requirements
specify coordination between environmental processes;
3) the level of technical detail required for
conformity analyses meets or exceeds the level already required for NEPA;
4) unless conformity is
taken into account, alternatives and mitigation measures generated
during the NEPA analytical process
may later result in a negative conformity determination; and
5) public comment periods, unless
coordinated, would run consecutively rather than concurrently, potentially delaying project
The consequences of a more mobile population include air pollution, health effects, poor visibility,
greenhouse gas emissions, and ozone layer depletion.
In recognition of these problems, the United
States has developed legislation to regulate transportation activity in consideration of the environment.
Some legislation is focused directly on reducing the environmental impacts of the transportation
system, such as the mobile source provisions of the 1970 Clean Air Act (CAA) and its subsequent
amendments that require cleaner vehicles and the implementation of transportation control measures
Other legislation focuses on transportation planning and development processes, primarily to
Institute of Transportation Studies, University of California at Davis, Davis, CA
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA