By Ginika Igboke
The Environmental Protection Agency (EPA) has partially disapproved a California regulation that would impose strict emissions standards on heavy-duty vehicles operating in the state, regardless of where those vehicles are registered, the agency announced in a Jan. 27 statement.
At the center of the dispute is California’s Heavy-Duty Inspection and Maintenance (I/M) Regulation, adopted under the Clean Air Act (CAA). The rule requires heavy-duty vehicles to undergo periodic emissions testing and comply with other requirements to ensure their emission control systems are functioning properly, according to the California Air Resources Board (CARB).
The regulation applies to nearly all non-gasoline vehicles with a gross vehicle weight rating above 14,000 pounds, excluding zero-emission vehicles. CARB stated that the requirements cover all vehicles operating on California’s public roads and highways, “even if they are not registered in California.” The rule began a phased implementation in 2023.
CARB submitted the I/M regulation to the EPA in December 2022 as a revision to its State Implementation Plan (SIP), which outlines how a state will meet federal air quality standards under the CAA. The EPA is required by law to review and approve such plans.
In its decision, the EPA said California’s attempt to apply the I/M program to all heavy-duty vehicles traveling through the state is “unprecedented” and may violate federal law. The agency determined that California failed to provide the assurances required under Section 110 of the CAA that the regulation would be consistent with the U.S. Constitution’s Commerce Clause, which limits state interference with interstate and international trade.
As a result, the EPA approved the I/M program only for vehicles registered in California and disapproved its application to vehicles registered outside the state.
CARB maintains that the CAA gives it authority to develop statewide programs aimed at reducing toxic emissions from mobile sources, noting that heavy-duty diesel vehicles weighing more than 14,000 pounds are major contributors to California’s air pollution. The board estimates that, once fully implemented, the I/M regulation would reduce nitrogen oxide emissions by more than 81 tons per day and particulate matter emissions by 0.7 tons per day statewide by 2037. CARB has projected that these reductions could prevent more than 7,500 premature deaths.
The EPA, however, emphasized in a policy document that unlike previous CARB rules, the I/M regulation would apply to out-of-state and even out-of-country vehicles operating in California for “almost any length of time.” According to the agency, this would shift the costs of emissions reductions onto vehicles registered outside California, while the state would receive localized environmental benefits.
The EPA stated that the Clean Air Act does not allow states to impose the costs of in-state emissions reductions on other states unless explicitly authorized by Congress.
EPA Administrator Lee Zeldin criticized the rule, saying the agency would not allow California to impose regulations with nationwide economic consequences. He warned that such policies could raise costs for truckers and businesses across the country, driving up prices for consumers. Zeldin added that voters supported policies focused on affordability and economic growth rather than nationwide adoption of California’s regulatory approach.
CARB did not respond to a request for comment by publication time.
The decision comes as the EPA signals a broader reevaluation of federal emissions regulations. In July, the agency proposed rescinding its 2009 Endangerment Finding, which serves as the legal basis for regulating greenhouse gas emissions from vehicles. The EPA has argued that such climate regulations impose significant costs on U.S. manufacturers and limit affordable vehicle options for consumers.
Earlier this month, the proposal to reconsider the Endangerment Finding was submitted to the Office of Management and Budget for review.
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