Attorney General Bonta Slams EPA’s Proposed Rule to Weaken Regulation of Heavy-Duty Vehicle Pollution

OAKLAND - California Attorney General Rob Bonta and the California Air Resources Board (CARB) led a multistate comment letter opposing the U.S. Environmental Protection Agency's (EPA) proposal to loosen regulations that control the emissions of smog-forming nitrogen oxides (NOx) from semi-trucks and other heavy-duty vehicles. If finalized, EPA's proposed rule would harm public health and welfare by contributing to air pollution that causes harmful health effects and generally contributes to poor air quality, particularly in environmental justice communities. In the comment letter, the coalition argues that EPA should withdraw its proposal, as it fails to comply with the statutory requirements of the Clean Air Act.

"The EPA's harmful rule is not only illegal, but it would put public health at risk by contributing to dangerous air pollution with serious health impacts. These impacts are especially concerning for communities of color and low-income communities, which too often bear a disproportionate share of pollution and its health consequences," said Attorney General Bonta. "The Trump Administration should be strengthening protections against vehicle pollution, not weakening them. That's why we are urging them to withdraw this illegal rule immediately."

The transportation sector is the largest source of NOx emissions in the United States, with heavy-duty vehicles being the second-largest contributor within that sector. Exposure to pollutants like NOx is associated with a range of adverse respiratory effects, including asthma, respiratory inflammation, and decreased lung function and growth. Communities of color and low-income communities, who disproportionately live, work, or attend school near major roadways and other NOx pollution sources like railyards, ports, and warehouses, are most vulnerable to this pollution and the resulting health impacts.

In July 2026, EPA published its proposed rule, which, if finalized, would revise a number of emission regulations for heavy-duty vehicles published in 2023 under President Biden. EPA's proposed rule specifically attempts to roll back key regulations that greatly reduce the emission of NOx from commercial vehicles. For example, the proposed rule would:

• Shorten the emission warranty period for heavy-duty vehicles from 10 years to 5 years for model year (MY) 2027 and later vehicles, which by the agency's own calculations would result in an additional 36,000 tons of NOx emissions annually.
• Delay the implementation of the 2023 Rule's longer regulatory useful life periods from MY 2027 to MY 2030. This change would result in increased NOx emissions by shortening the period over which emission standards apply to heavy-duty vehicles.
• Weaken key regulatory inducements that ensure that emission control systems are properly maintained and functioning.

In the comment letter, the coalition explains that the proposed rule, if finalized, would violate the law by undermining separately-required emissions standards for heavy-duty vehicles, impairing states' and cities' efforts to meet federally-mandated air quality standards, and by failing to consider the health consequences of increased pollution from the rule. The coalition urges EPA to withdraw the proposed rule immediately.

In submitting the comment letter, Attorney General Bonta and CARB lead the attorneys general of Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, New York, North Carolina, Oregon, Rhode Island, Washington, Wisconsin, the District of Columbia, and the Chief Legal Officers of the City of Chicago, Illinois; the City and County of Denver, Colorado; the City of New York, New York; and the City and County of San Francisco, California.