A unanimous Supreme Court has held that the Federal Motor Carrier Safety Administration (FMCSA) did not violate U.S. environmental law by failing to conduct an environmental impact statement (EIS) of increased pollution from allowing Mexican trucks to operate in the United States beyond limited border zones. The Court's decision reversed an opinion of the Ninth Circuit Court of Appeals requiring FMCSA to consider the pollution increase in a full EIS prior to issuing regulations governing applications and safety inspections for Mexican trucks to operate in the United States. In response to discriminatory treatment of U.S. trucking operations in Canada and Mexico, Congress imposed a moratorium in 1982 on new permits for motor carriers in Canada and Mexico to operate in the United States. Set to expire after two years, the moratorium law permitted the White House to extend the ban for additional two-year increments. The moratorium on Canadian operations was ended quickly, but the Mexican moratorium was extended throughout the 1990s. When the United States signed the North American Free Trade Agreement (NAFTA) with Mexico and Canada in 1992, the U.S. government agreed to pull back on the moratorium. Mexican motor carriers were allowed to conduct some bus services in 1994, but lingering safety concerns led the White House to postpone lifting the ban on Mexican trucks. The Mexican government used NAFTA's dispute resolution process to challenge the remaining portion of the moratorium, and an arbitration panel ruled in 2001 against the U.S. position. President Bush subsequently announced he intended to lift the moratorium and the FMCSA published proposed rules that both created an application form for Mexican trucks seeking to operate in the larger United States and established a related safety inspection system. Congress then demanded that the Department of Transportation not spend any of its appropriations to permit Mexican trucks to operate beyond border zones until FMCSA implemented certain application and safety monitoring requirements, some of which were more extensive than the FMCSA's proposed rules. FMCSA revised its regulations but opted not to conduct a comprehensive environmental impact statement. Instead, it declared there would be no significant environmental impact warranting an EIS. FMCSA prepared a less comprehensive environmental assessment for the application and one of the safety monitoring rules, excluding its rule for certifying safety inspectors altogether from environmental review. FMCSA also failed to determine whether any of the proposed regulations complied with the Clean Air Act because, it maintained, the proposed rules fell within certain categorical exemptions from the requirement of determining conformity with the Clean Air Act. A number of public interest groups and intervenors, including Public Citizen and the Natural Resources Defense Council, petitioned the Ninth Circuit challenging the validity of FMCSA's proposed rules. The appeals court href="http://www.ca9.uscourts.gov/ca9/newopinions.nsf/564D4A580B7317BE88256CB0000D6E A2/$file/0270986.pdf?openelement">held that FMCSA violated both the National Environmental Policy Act of 1969 (NEPA) and the Clean Air Act (CAA) by failing to consider the increase in traffic and pollution that would result. The circuit court reasoned that the White House's lifting of the moratorium was a reasonably foreseeable consequence of FMCSA's regulations, in part because the White House had clearly signaled its intent to do so as soon as FMCSA issued appropriate regulations. More significantly, Congress' separate application and safety monitoring requirements had made FMCSA rulemaking effectively a condition precedent of terminating the moratorium. The Ninth Circuit reasoned FMCSA was required to consider the significant increase in traffic and pollution emissions, which were the reasonable foreseeable indirect effect of FMCSA's rules, and which therefore triggered both NEPA's requirement for a full EIS and CAA's requirement for a conformity determination. The Supreme Court href="http://www.supremecourtus.gov/opinions/03pdf/03-358.pdf">disagreed, holding that FMCSA's rulemaking should not be considered a proximate cause of either the moratorium's end or the resulting emissions increase. "Proximate cause" is a concept imported from tort law, which limits the extent to which an event can be held legally to be the cause of effects which follow in an attenuated chain of events. Justice Thomas, writing on behalf of a unanimous court, reduced the fact of increased traffic to the fact of the White House ending the moratorium. Because FMCSA could neither end the moratorium (as only the White House itself could end it) nor prohibit Mexican trucks altogether once the moratorium was ended, FMCSA's rules could not, according to Thomas, be treated as the proximate cause of the inrush of Mexican trucks or the resulting pollution. The opinion is at times opaque, and that opacity makes the ultimate effect of the holding uncertain. For example, it is unclear how the FMCSA's inability to exclude all Mexican trucks categorically from U.S. operations is relevant to the logic of the opinion and, therefore, to the future applicability of the decision. Thus, although the Court appears to have made the proximate cause requirement of administrative challenges more stringent, the extent to which proximate cause has been heightened is unclear. Further, when the Court rejected the challengers' argument that the FMCSA should have considered alternatives to mitigate environmental damage from the newly-permitted trucks on the basis that the public interest groups failed in the formal comment period to specify any alternatives or to urge FMCSA to consider any alternatives, thus losing the right to pursue that argument in the judicial challenge, the Court did not elaborate how the failure to preserve that objection squares with its later assertion that an environmental analysis can be so obviously inadequate that a flaw need not be identified in the formal comment period in order to be raised in a court challenge. The opinion merely states, conclusorily, "But that situation is not before us." Finally, the Court did not consider the argument that safety requirements can have environmental consequences. Insisting that the public interest groups "fail to identify any evidence that shows that any effect from" possibly more stringent safety rules "would be significant, or even noticeable, for air-quality purposes" and that the link between safety regulation and environmental damage "is also tenuous at best," the Court left unclear the extent to which such substantive proof is required for a claim of procedural insufficiency.