Skip to main content
Nossaman LLP


D.C. Circuit Issues Split Decision In Clean Air Act Challenge to Regional Transportation Plan Conformity Regulations

By: Robert D. Thornton, Stanley S. Taylor

In the latest in a series of environmental group challenges to the EPA’s transportation conformity regulations issued under the Clean Air Act (the "Act")[1], the D.C. Circuit Court of Appeals has handed the EPA a mixed decision.  In Environmental Defense v. EPA, 2006 U.S. App. LEXIS 26000 (D.C. Cir. Oct. 20, 2006), the Court invalidated a regulation that established an interim test for determining conformity to more stringent ozone standards adopted by the EPA.  The Court also rejected a challenge to the so-called "build/no build test" for determining conformity of transportation plans and programs to state air quality implementation plans ("SIPs").  Finally, on procedural grounds, the Court rejected a challenge to regulations establishing the criteria for determining that a transportation plan, program and project are consistent with the SIP’s motor vehicle emissions budget.


By rejecting the EPA’s "interim SIP" requirement and requiring states and the EPA to amend SIPs to incorporate the new ozone standards, the decision gives Metropolitan Planning Organizations ("MPOs") and sponsors of transportation projects additional time to comply with the more stringent national ambient air quality standards.  And, by affirming the EPA’s alternate "build/no build" test, the court has given MPOs additional flexibility to adopt transportation plans incorporating projects that do not necessarily reduce emissions, so long as the SIP overall results in the required emission reductions. 


The 1990 Clean Air Act Amendments[2] revised the air quality requirements applicable to the approval of transportation plans, program and projects.  In general, the Amendments established more rigorous procedures and standards governing determinations that transportation plans, programs and projects are in conformity with SIPs.  The Amendments, and regulations adopted by EPA to implement the regulations, have spawned a number of lawsuits around the nation challenging transportation plans and projects on air quality grounds.

At the federal level, the Act requires the EPA to promulgate National Ambient Air Quality Standards ("NAAQS") that promote public health by establishing maximum limits for various air pollutants.  The EPA is authorized to revise NAAQS or to promulgate new NAAQS to reflect changed conditions and new scientific understanding.  New or revised NAAQS must be incorporated into SIPs.


The decision addresses the EPA’s regulations that implement the Act’s conformity requirements. 

A.      Challenge to Interim Test for New Ozone Standard (40 C.F.R. Section 93.109(e)(2)(v))

The Court concluded that these regulations, which established interim tests for demonstrating conformity  to newly revised ground level ozone NAAQS, violated the requirement that conformity be determined with respect to an applicable implementation plan in effect—in other words, an approved SIP.  Since the interim standards, which reflected a heightened requirement for ozone attainment, had not been formally adopted through the SIP process, the Court concluded that the rulemaking violated the Act’s requirement that conformity be based on an approved implementation plan, and therefore that the regulations in question were invalid.

B.      Challenge to "Build/No Build" Test (40 C.F.R. Section 93.119(b)(2), (d) and (e))

These regulations provided that in certain nonattainment areas[3], a conformity determination may be made using one of two interim tests.  Under the regulations, the MPO may demonstrate that a transportation plan conforms to the Act if the plan passes either a "build/no build" test or a "baseline year" test.  Under the first test, a plan or project conforms to the Act if it will not result in additional total emissions from the nonattainment area.  Under the second test, a plan or project conforms if the total emissions from the area, including emissions added by the plan or project, will not exceed emission limitations set in prior years.  In some ozone nonattainment areas, both tests must be met.

The challengers argued that the build/no build test violated the Act in nonattainment areas insofar as it allowed transportation plans that do not reduce mobile source emissions to be deemed conforming.  They urged that the rule ran afoul of the purpose of such plans to eliminate or reduce violations of NAAQS and to achieve expeditious attainment of such standards.  They concluded that this requirement mandated that every transportation plan must result in mobile source emission reductions in order to show conformity to the SIP.

The Court rejected these arguments, however, concluding that SIP conformity can be demonstrated by using the build/no build test, even if individual transportation plans do not actively reduce emissions; the Court observed that the Act is "notably silent" on whether the transportation plans themselves, which are only a part of the SIP, must reduce emissions.  Since the Act is silent, the EPA may exercise its discretion in construing the requirement.  Since mobile source emissions represent only a portion of total emissions (the balance coming from stationary sources), a SIP could reduce overall emissions by reducing stationary source emissions only.  Absent language in the Act requiring transportation plans to actively reduce mobile source emissions, the EPA’s "reasonable interpretation" of the Act was upheld.

C.      Challenge to Motor Vehicle Emissions Budget Criteria.  (40 C.F.R. Section 93.118(b), (d) and (e)(6))

The environmental petitioners challenged these regulations, which establish procedures for determining whether transportation plans and programs are consistent with the motor vehicle emissions budget in a SIP.  The Court rejected the environmental group’s challenge on the grounds that the statute of limitations for the challenge had expired.

For more information, contact Robert D. Thornton at (949) 833-7800 / or Stanley S. Taylor at (415) 438-7224 /

[1]     42 U.S.C. § 7401 et. seq.; 40 C.F.R. Part 93.

[2]     Pub. L. 101-549.

[3]     Nonattainment areas are those areas that are not in compliance with the federal clean air standards.

  • Professionals
  • Practices
  • Success Stories
  • News
  • Events
  • Resources
  • Firm Pages