The U.S. Department of Transportation has filed suit against the California Air Resources Board claiming CARB has adopted and enforced their own state standards for light-duty vehicles in violation of federal law.

The complaint states that only the National Highway Traffic Safety Administration is authorized to establish uniform, nationwide vehicle fuel-economy standards, and that Congress stated its preference for national uniformity by expressly preempting any state laws and regulations that are “related to fuel economy standards” for vehicles covered by federal fuel economy standards.

The complaint further asserts the regulations impose requirements on vehicle manufacturers that limit fleetwide tailpipe carbon dioxide emissions on the purported ground of reducing global climate change and include zero-emission vehicle mandates that establish a de facto market share quota for electric vehicles.

Although the CARB regulations do not establish fuel economy standards for medium- or heavy-duty vehicles, allowing CARB to enforce these states requirements for automobiles and light trucks would set a precedent for the state’s adoption of additional fuel economy standards for heavier vehicles.