SACRAMENTO — California’s efforts to limit pollution from diesel-powered trains and big rigs were stalled in anticipation of pushback from the incoming Trump administration.

The California Air Resources Board said Tuesday it withdrew its requests for federal approval to implement stricter emissions rules for locomotives and semi-trucks because the U.S. Environmental Protection Agency had yet to approve them. The decision came just days before Democratic President Joe Biden leaves office.

Trump’s Previous Opposition to California Climate Efforts

During his first administration, Trump attempted to thwart various California climate efforts, including rules to cut down on greenhouse gas emissions from transportation sources.

One of the rules California pulled after the EPA failed to approve it would have phased out the sale of new diesel-powered semi-trucks and buses by 2036. The Air Resources Board passed the regulation in 2023. Another rule, which the agency approved the same month, would have banned locomotive engines more than 23 years old by 2030 and increased the use of zero-emissions technology to transport freight from ports and throughout railyards.

Both rules were opposed by industry as costly mandates that would be difficult to implement.

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Air Resources Board Assessing Options

Air Resources Board Chair Liane Randolph said the agency is assessing its options to continue its efforts to curb planet-warming emissions and improve air quality but did not offer specifics on what comes next.

“While we are disappointed that U.S. EPA was unable to act on all the requests in time, the withdrawal is an important step given the uncertainty presented by the incoming administration that previously attacked California’s programs to protect public health and the climate and has said will continue to oppose those programs,” Randolph said in a statement.

Mike Alpern, a spokesperson for the EPA’s Pacific Southwest region, said the agency would not take any further action on the rules.

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California’s Authority to Set Stricter Emissions Standards

California has long had the authority to set emissions standards that are stricter than federal rules. During Trump’s first term, his administration challenged that authority. But a federal court last year upheld California’s ability to set nation-leading vehicle emissions regulations. The EPA granted California the authority last month to enforce a rule banning the sale of new gas-powered cars in the state by 2035.

Karoline Leavitt, a spokesperson for Trump’s transition team, did not comment on California pulling its waiver requests but said the incoming president would work to improve air and water quality during his second presidency.