The Environmental Protection Agency has proposed to disapprove the California Air Resources Board's Heavy Duty Vehicle Inspection and Maintenance Program to the extent it applies to vehicles registered outside of California.

Under the Clean Air Act, CARB had submitted to EPA a revised State Implementation Plan (SIP) relating to the control of emissions from non-gasoline combustion vehicles over 14,000 pounds. EPA is proposing to disapprove the state's ''Heavy-Duty Inspection and Maintenance Regulation'' to the extent it applies to vehicles registered out-of-state or out-of-country.

Under the proposed revisions to the SIP, which incorporates California's standards for Heavy-Duty Remote On-Board Diagnostic Devices, operators of vehicles over 14,000 lbs. GVW in California must report owner and vehicle information to CARB. They must also periodically test vehicles and submit test results to CARB, have a HD I/M compliance certificate on board the vehicles, and be subject to roadside monitoring and field inspections.

EPA questions whether applying these requirements to vehicles from outside the state that operate into or through California, which amounts to about one half of the heavy-duty vehicles in the state, violates the Commerce Clause of the U.S. Constitution. The Clean Air Act provides that a SIP must include "necessary assurances" that the state "is not prohibited by any federal or state law from carrying out such implementation plan or portion thereof."

EPA asserts that approving the SIP would delegate to California the ability to enforce the state's I/M requirements throughout the nation to the extent a vehicle passes through or operates within the state for almost any length of time. As a result, an approval would effectively force regulated entities in other states to comply with California's HD I/M requirements, rather than the applicable requirements in their respective states, including requirements approved by the EPA pursuant to the CAA.

The EPA notice estimates the cost of compliance with the CARB HD I/M standards at between $772 to $2,180 annually for a typical fleet of seven vehicles. These costs relate to HD vehicle testing, repair, and compliance fees.