The Environmental Protection Agency finalized a partial approval and partial disapproval of California's submission to revise its State Implementation Plan on February 6, 2026. The action incorporates the state's Heavy-Duty Inspection and Maintenance Regulation into the federally enforceable air quality plan but limits its scope to vehicles registered within California. This decision stems from concerns that extending the program to out-of-state and foreign vehicles violates federal law, including the Commerce Clause of the U.S. Constitution and provisions of the Clean Air Act. Occurring amid California's ongoing efforts to meet national air quality standards, the ruling underscores the challenges of balancing local pollution reduction needs with national commerce protections. By restricting the program's reach, the EPA aims to prevent undue burdens on interstate trucking while allowing California to credit emissions reductions from in-state vehicles toward attainment goals.
Background and Regulatory Context
California submitted the Heavy-Duty Inspection and Maintenance Regulation to the EPA on December 14, 2022, following its adoption by the California Air Resources Board on August 22, 2022. The regulation targets non-gasoline heavy-duty vehicles over 14,000 pounds, requiring periodic emissions testing, reporting, and compliance certificates to ensure functional emissions control systems. It replaces older programs like the Heavy-Duty Vehicle Inspection Program and Periodic Smoke Inspection Program, building on them with on-board diagnostic testing for newer vehicles and smoke opacity checks for older ones.
Under the Clean Air Act, states must submit plans to implement national ambient air quality standards, particularly in nonattainment areas for pollutants like ozone and particulate matter. California's program addresses significant emissions from heavy-duty vehicles, which CARB estimates contribute 52 percent of on-road nitrogen oxides and 54 percent of fine particulate matter statewide. The regulation's novelty lies in its intended application to out-of-state and foreign vehicles operating in California, even briefly, aiming to capture reductions from sources responsible for about 30 percent of heavy-duty nitrogen oxide emissions in the state.
Key players include CARB as the submitting agency, the EPA under Administrator Michael Regan, and stakeholders like trucking associations and environmental groups who commented during the rulemaking. The action follows a proposed rule on August 26, 2025, which solicited input on full approval versus partial disapproval.
Legal and Constitutional Analysis
The EPA's decision hinges on Clean Air Act section 110(a)(2)(E)(i), requiring states to provide 'necessary assurances' that plan implementation is not prohibited by federal or state law. California failed to assure that applying the regulation to out-of-state vehicles complies with the Commerce Clause, which prohibits states from unduly burdening interstate commerce.
Citing Supreme Court precedents like National Pork Producers Council v. Ross (2023) and Pike v. Bruce Church, Inc. (1970), the EPA noted that the regulation imposes significant costs—estimated at $4.12 billion from 2023 to 2050—on interstate trucking, an instrumentality of commerce. These burdens, including testing and downtime, outweigh localized benefits to California's air quality, potentially violating the dormant Commerce Clause by externalizing attainment costs to other states. The agency also raised concerns about foreign relations powers, as the program affects vehicles from Mexico and Canada, intruding on federal authority.
Public comments revealed practical burdens: out-of-state operators face higher compliance costs due to limited access to CARB-approved testers, risking fines up to $10,000 per day. Trucking groups like the American Trucking Associations argued this creates a de facto national standard, conflicting with other states' programs in New York, New Jersey, and Oregon.
Environmental advocates, including the Union of Concerned Scientists, countered that benefits like 81 tons per day of nitrogen oxide reductions by 2037 justify the program, but the EPA found these insufficient to overcome legal hurdles.
Implications for Air Quality Planning
Short-term, the partial approval credits emissions reductions from in-state vehicles toward California's attainment demonstrations in areas like the South Coast Air Basin and San Joaquin Valley, where heavy-duty sources dominate pollution. CARB projects 22 tons per day of nitrogen oxide cuts in the South Coast by 2037, aiding ozone and particulate matter goals.
Long-term, the disapproval may force California to seek alternative reductions from stationary sources or in-state mobile controls, potentially delaying attainment. It sets a precedent for limiting state overreach in SIPs, encouraging uniform federal approaches under Clean Air Act sections 202 and 209. Perspectives differ: trucking interests view it as protecting commerce, while environmental groups warn of weakened pollution controls, possibly shifting burdens to federal programs.
No sanctions or federal implementation plans result, as the submission is discretionary. The ruling aligns with executive actions under President Trump, emphasizing deregulation in interstate contexts.
Key Takeaways and Future Outlook
This action reinforces the Clean Air Act's framework, where states regulate within borders but must assure federal compliance. It highlights ongoing debates over state authority in a federal system, with potential challenges in court or revisions by CARB to address out-of-state concerns. Future steps may include California submitting revised controls or the EPA facilitating interstate agreements, amid broader discussions on national emissions standards.
