The U.S. Environmental Protection Agency on Tuesday, Jan. 27, announced its final disapproval of California’s Heavy-Duty Inspection and Maintenance (HD I/M) regulation as it applies to trucks registered out-of-state.
The HD I/M regulation truck owners may more readily remember as the Clean Truck Check or “smog check” rule. It has required truck owners to conduct emissions tests and pay a compliance fee since 2023, and applies to all non-gasoline combustion vehicles above 14,000 gross vehicle weight rating (GVWR) that operate in California.
The compliance fee was initially $30 and is tied to the California Consumer Price Index. As of Jan. 1, 2026, the fee is now $32.13.
Under the regulation, vehicles equipped with onboard diagnostic (OBD) systems can be tested using OBD data, while older non-OBD vehicles are subject to smoke opacity and visual inspections. Vehicle owners are required to have a valid rule compliance certificate with the vehicle while operating in California, which they must present to a CARB inspector and/or California Highway Patrol officer upon request.
California submitted its Clean Truck Check regulation to the EPA as part of a revised State Implementation Plan -- required for every state to outline states’ plans for implementing, maintaining and enforcing EPA’s national ambient air quality standards. After receiving a state plan, the EPA determines if the submission meets all applicable Clean Air Act requirements.
State plans approved by EPA become federally enforceable under the Clean Air Act.
[Related: California puts teeth in emission regs with new 'smog check' system]
The California Air Resources Board (CARB) submitted the HD I/M regulation as a revision to the California plan more than three years ago, on Dec. 14, 2022. In its Jan. 27 decision, EPA partially approved and partially disapproved the regulation.
Approval was limited to application of the rule to in-state registered vehicles. EPA disapproved the regulation's application to vehicles registered in other states or countries.
“The Trump EPA will never back down from holding California accountable and stopping them from imposing unnecessary regulations on the entire nation,” said EPA Administrator Lee Zeldin. “If California had its way, prices would skyrocket for truckers and businesses across America. Affordable trucks are vital for keeping food and goods moving and prices low for families. Americans didn’t vote for California’s policies to be imposed nationwide. They voted for President Trump’s policies that put working families first.”
CARB, however, said it will continue to enforce the regulation in full at the state level, calling the EPA's announcement a "whole lot of bluster about bean counting,” said CARB Director of Communications Lindsay Buckley. “EPA has no authority over this program, and we will continue to enforce the law to ensure that all trucks coming into and operating in California abide by the same rules -- even if EPA doesn’t want to give us credit.”
EPA’s notice of partial disapproval makes clear that California may continue enforcing the regulation at the state level. Because the submittal of the HD I/M regulation was discretionary and not a required part of the State Implementation Plan, EPA will not impose any sanctions on California under the Clean Air Act. Federal promulgation of an implementation plan isn't necessary “because the partial disapproval does not reveal a deficiency" in California's plan that a federal plan "must correct," according to EPA.
As such, the regulation “has been adopted by the State of California, and our partial disapproval will not by its own force prevent the State from enforcing it within California as a matter of State law,” EPA said.
[Related: CARB problems: untangling state and federal emissions regulations]
Why EPA won’t enforce the rule federally
For EPA to approve a state plan, the Clean Air Act requires “necessary assurances” that the state “is not prohibited by any Federal or State law from carrying out” implementation of the plan.
Disapproving enforcement against non-California-registered vehicles, EPA determined “that California has not provided necessary assurances that the State is not prohibited by Federal law -- specifically, the Clean Air Act and the Commerce Clause of the U.S. Constitution -- from implementing the HD I/M Regulation to the extent it purports to regulate vehicles registered out-of-state or out-of-country based solely on whether such vehicles traverse California for virtually any length of time.”
EPA said the HD I/M regulation “arguably discriminates against out-of-state vehicle owners and operators" by adding costs to out-of-state businesses to achieve "local benefits" of air quality standards attainment.
The agency added that nothing in the regulatory goals of the HD I/M rule required California to extend compliance requirements beyond California-based vehicles. Instead, EPA said the state could have limited the regulation’s application to California-registered vehicles and adopted additional emissions controls on those vehicles to achieve progress toward air-quality standards attainment without raising interstate commerce concerns.
“The choice to extend the regulation to out-of-state and out-of-country vehicles was deliberate and unnecessary to the operation of the regulatory scheme with respect to vehicles registered within the State,” EPA added.
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Had EPA approved the California plan, the agency said it would have required out-of-state/country vehicle owners to comply “given the volume of interstate trucking that passes through California, the uncertainties regarding whether and when a route will cross through California over the course of a year, and the significant penalties associated with failure to comply.”
The agency added that if it approved the state plan, the Clean Truck Check rule “would, in effect, become a Federal regulation enforceable by the EPA (and citizen-suit plaintiffs) against any owner or operator in all fifty States of any heavy-duty vehicle that may pass through California.” The result, EPA noted, would be additional compliance costs for heavy-vehicle operators in all jurisdictions across the U.S.
In addition to potential Clean Air Act and Commerce Clause violations for applying the regulation to trucks registered out-of-state, EPA said enforcing the regulation for trucks registered out-of-country could violate foreign relations powers provisions of the U.S. Constitution.
[Related: Court halts CARB/OEMs' Clean Truck Partnership as dueling lawsuits play out]
