California has decided to abandon its groundbreaking regulations phasing out diesel trucks and requiring cleaner locomotives because the incoming Trump administration is unlikely to allow the state to implement them.

State officials have long considered the rules regulating diesel vehicles essential to cleaning up California’s severe air pollution and combating climate change.

The withdrawal comes after the Biden administration recently approved the California Air Resources Board’s mandate phasing out new gas-powered cars by 2035, but had not yet approved other waivers for four diesel vehicle standards that the state has adopted.

President-elect Donald J. Trump has threatened to revoke or challenge all zero-emission vehicle rules and California’s other clean-air standards. By withdrawing its requests for U.S. Environmental Protection Agency approval, the Newsom administration is signaling a dramatic step back as the state recalibrates in anticipation of the new Trump era.

“California has withdrawn its pending waiver and authorization requests that US EPA has not yet acted on,” Liane Randolph, Air Resources Board Chair, said in a statement. “While we are disappointed that US 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.”

Environmentalists said the move would put communities at risk and dismantles key programs.

“Diesel is one of the most dangerous kinds of air pollution for human health, and California’s diesel problem is big enough to cast its own shadow,” said Paul Cort, director of the group Earthjustice’s Right To Zero campaign.

California’s Advanced Clean Fleet rule, which phases out diesel trucks, was one of the most far-reaching and controversial rules that California has enacted in recent years to reduce air pollution and greenhouse gases. It would have ended the sale of new fossil-fuel trucks in 2036 and required large trucking companies to convert their medium and heavy-duty fleets to electric or hydrogen models by 2042.

Trucking companies sued the state to stop the measure, saying electric and hydrogen big rigs are not practical for long-haul uses and that it would destroy the state’s economy.

Diesel exhaust has been linked to cancer and contains fine particles that can trigger asthma and heart attacks as well as gases that form smog. Low-income, disadvantaged communities of color near ports, freeways and warehouses, especially in the Los Angeles and Long Beach area, have long complained about noxious and dangerous diesel exhaust.

The state withdrew three other measures regulating emissions from diesel-powered locomotives , commercial harbor craft and refrigeration unit engines that are hauled by trucks and rail cars.

The truck fleet rule would have affected about 1.8 million medium and heavy-duty trucks on California roads, including delivery trucks used by FedEx, UPS and Amazon.

Some provisions, for drayage trucks that serve ports, were supposed to be implemented already, but the air board put them on hold pending the outcome of the Biden administration’s approval.

Some companies, including Pepsi , have already rolled out electric and hydrogen fleets. Amazon has deployed 50 heavy-duty electric trucks in Southern California as well as hundreds of electric vans nationally. Sales of zero-emissions trucks have increased despite no deadlines kicking in. In 2023, one out of every six medium and heavy-duty trucks sold in the state — more than 18,000 — were zero emissions.