EPA proposal challenges CARB’s Clean Truck Check program

Purpose of the CTC regulation

The regulation aims to reduce emissions of nitrogen oxides (NOₓ) and particulate matter (PM), which are significant contributors to air pollution and health risks.

Heavy-duty vehicles, though only 3 percent of California’s fleet, contribute over 50 percent of on-road NOₓ and PM emissions.

The rule is part of California’s broader effort to meet federal air quality standards.

Key provisions of CTC

The Clean Truck Check program:

• Requires emissions testing and compliance certification for heavy-duty vehicles operating in California.
• Applies to in-state and out-of-state vehicles, with limited exemptions (e.g., emergency vehicles, zero-emission vehicles).
• Establishes a referee testing network and roadside inspection protocols.
• Requires that proof of compliance be carried in vehicles and test results be submitted periodically.

EPA’s proposal

EPA’s proposal indicates support for the regulation as it applies to California-registered vehicles, finding it consistent with Clean Air Act requirements.

However, the agency notes legal and constitutional concerns about the regulation’s application to out-of-state and international vehicles.

The EPA proposes to:

• Approve the regulation for California-registered vehicles.
• Disapprove the regulation as it applies to out-of-state and out-of-country vehicles.

Public participation

The EPA seeks public comment on the proposal, including:

• The legality of applying the rule to non-California vehicles, and
• Potential impacts on interstate commerce and other states’ regulatory authority.

Comments are due by September 25, 2025. Submit your comments, identified by Docket ID No. EPA-R09-OAR-2025-0061 at https://www.regulations.gov.