## Facts

- Federal law temporarily barred Mexican motor carriers from obtaining operating authority in the United States, while authorizing the President to lift that restriction.
- The President announced an intent to lift the restriction once new safety-related regulations were in place for Mexican carriers.
- The Federal Motor Carrier Safety Administration (FMCSA) issued rules addressing application procedures and a safety-inspection regime for Mexican motor carriers.
- FMCSA prepared an Environmental Assessment (EA) and issued a Finding of No Significant Impact (FONSI), declining to analyze environmental effects from an increased volume of Mexican trucks on the ground that any increase would result from the President’s lifting of the restriction rather than from FMCSA’s safety rules.
- Under the Clean Air Act (CAA), FMCSA concluded the rules would not trigger a full “conformity” determination because any emissions increases would fall below applicable regulatory thresholds.
- Public-interest and environmental groups sought judicial review, arguing the EA unlawfully omitted the environmental effects of increased cross-border truck traffic and that FMCSA was required to conduct a full CAA conformity determination.
- The Ninth Circuit agreed and ordered FMCSA to prepare an Environmental Impact Statement (EIS) and to make a full conformity determination.

## Issues

1. Under NEPA, whether FMCSA had to analyze environmental effects from increased Mexican truck traffic when those effects would occur due to the President’s separate decision to lift the statutory restriction.
2. Under the CAA, whether FMCSA’s rules required a full conformity determination with state implementation plans.

## Decision

- The Supreme Court unanimously reversed the Ninth Circuit.
- The Court held FMCSA did not violate NEPA by limiting its EA to effects proximately caused by FMCSA’s own rules and within FMCSA’s statutory authority to prevent.
- The Court concluded that any increase in Mexican truck traffic would be legally attributable to the statutory scheme and the President’s decision to lift the restriction, not to FMCSA’s safety regulations.
- The Court rejected the view that reasonable foreseeability or “but-for” causation alone required FMCSA to evaluate the environmental impacts of increased truck traffic.
- The Court also held FMCSA was not required to conduct a full CAA conformity determination based on emissions effects attributable to independent decisions outside FMCSA’s control.

## Legal Principles

- NEPA requires analysis of environmental effects only when they are proximately caused by the challenged agency action and are within the agency’s authority to prevent or regulate.
- An agency is not required under NEPA to analyze environmental consequences of separate decisions by actors the agency cannot control, even if those consequences are foreseeable and the agency action is a precondition to the separate decision.
- “But-for” causation is insufficient, by itself, to make an environmental consequence an “effect” of agency action for NEPA purposes when the agency lacks relevant decisionmaking discretion.
- Under the CAA, an agency is not compelled to conduct a full conformity determination for emissions changes not directly caused by the agency’s action in a legally meaningful way, and may rely on applicable regulatory thresholds where appropriate.

## Conclusion

The Court held that FMCSA’s NEPA and CAA obligations were limited to impacts proximately caused by its safety regulations and within its statutory discretion, so FMCSA was not required to assess environmental effects attributable to the President’s decision to lift the restriction on Mexican motor carriers or to perform a full CAA conformity determination on that basis.


Dep't of Transp. v. Pub. Citizen, 541 U.S. 752 (2004)