EPA Proposes to Disapprove California’s “Clean Truck Check” Rule

On August 25, the U.S. Environmental Protection Agency (EPA) proposed to disapprove California’s “Heavy-Duty Inspection and Maintenance Regulation,” known as the Clean Truck Check rule. Developed by the California Air Resources Board (CARB) as a revision to the state’s implementation plan (SIP) under the Clean Air Act (CAA), the rule would establish periodic emissions testing for heavy-duty diesel and alternative-fuel vehicles over 14,000 pounds operating on California roads. EPA’s central concern is that the rule would apply not only to California-registered vehicles but also to trucks from out-of-state, raising issues of extraterritorial enforcement.

Under the CAA, EPA sets national ambient air quality standards (NAAQS) for criteria pollutants such as nitrogen oxides and particulate matter. States must adopt SIPs showing how they will attain and maintain those standards, and once approved by EPA, SIPs become federally enforceable. With several regions of California still in nonattainment, CARB argues the Clean Truck Check rule is critical to reducing emissions from heavy-duty vehicles, which account for more than half of the state’s on-road emissions. CARB projects that by 2037, the program would significantly reduce nitrogen oxides and particulate matter emissions tonnages, driving significant progress for attainment.

EPA, however, emphasized that this design effectively creates a backdoor emissions standard with nationwide implications, extending California’s regulatory authority beyond its borders. If finalized, EPA’s action would prevent California from establishing and enforcing the Clean Truck Check regulation. This outcome carries important implications for EMA companies that service California markets, as it would affect compliance planning and operational costs associated with fleet emissions monitoring.

More broadly, EPA’s proposed disapproval reflects ongoing tensions over federalism, preemption, and the limits of state authority in regulating vehicle emissions. The proposal is open for a 30-day public comment period, ending September 25, 2025. EMA will continue to track developments closely and advocate against regulations that restrict interstate commerce, disrupt fuel markets, or limit consumer choice.

See rule proposal here.