421 U.S. 60 (1975) (U.S. Supreme Court)
Train v. Natural Resources Defense Council is a foundational Clean Air Act decision that crystallizes the Act's cooperative federalism architecture.
Under the Clean Air Act, may EPA approve State Implementation Plans that use intermittent or supplementary controls rather than exclusively continuous, source-specific emission limitations to attain and maintain the national ambient air quality standards, or must EPA require states to use a particular form of emission limitation?
Under Clean Air Act § 110, states have primary responsibility to formulate SIPs that will attain and maintain the NAAQS. EPA must approve a SIP if it satisfies the Act's enumerated criteria (including attainment by statutory deadlines, enforceability, adequate monitoring, and compliance with other statutory requirements). The Act does not mandate that SIPs employ any particular form of emission limitation or categorically forbid intermittent or supplementary control strategies, and EPA may not impose additional, non-statutory requirements on states as a condition of SIP approval.
The Supreme Court reversed the D.C. Circuit and held that the Clean Air Act does not require EPA to mandate continuous, source-specific emission limitations or prohibit intermittent or supplementary controls in State Implementation Plans. States retain discretion to choose the mix of control measures, and EPA must approve SIPs that meet the Act's requirements, including timely attainment and enforceability, regardless of the specific techniques selected.
Train v. NRDC is a cornerstone of Clean Air Act cooperative federalism. It confirms that states may craft SIPs using a variety of control measures, and that EPA's role is to ensure compliance with statutory criteria rather than to dictate methods. For law students, the case illustrates statutory interpretation anchored in text, structure, and federalism principles; it also shows the limits of agency power to add prerequisites not found in the statute. The decision influenced Congress's subsequent 1977 Amendments, which, among other things, addressed concerns about certain dispersion techniques and added more detailed definitions—underscoring Train's practical impact on environmental legislation and policy design.