The Environmental Protection Agency has announced the agency’s final disapproval of California’s Heavy-Duty Inspection and Maintenance (I/M) Regulation under the Clean Air Act to the extent the regulation applies to out-of-state and out-of-country registered vehicles. EPA determined that California’s attempt to establish an I/M program in its State Implementation Plan (SIP) for heavy-duty vehicles that pass-through California, regardless of where the vehicle was registered, may violate Federal law.

Specifically, EPA determined that California failed to provide necessary assurances as required by Section 110 of the CAA, that implementing the regulation would be consistent with the U.S. Constitution’s Commerce Clause, which prevents states from interfering with interstate and international trade. EPA also said applying the regulation to out-of-state registered vehicles is not a proper use of the CAA’s planning provisions, which empower each state to promote air quality.

EPA’s approval was limited to the aspect of the regulation in California’s SIP only as it applies to in-state registered vehicles. EPA’s partial approval will allow the regulation to become federally enforceable for non-gasoline combustion vehicles over 14,000 pounds registered in California.