PRESIDENT TRUMP came into office promising to roll back rules designed to save energy and cut planet-warming greenhouse-gas emissions, including landmark regulations demanding better fuel economy from cars and trucks sold in the United States. Now, a year after federal officials began reviewing Obama-era car and truck rules, The Post’s Juliet Eilperin and Brady Dennis report that the Trump administration’s anti- ­regulation zeal may result in a far more aggressive rollback than even the auto industry wants.

The Obama rules demanded sharp increases in the overall fuel economy of vehicles sold in the United States, to 38.3 miles per gallon by 2018 and to 54.5 miles per gallon by 2025 for cars and light trucks, roughly double where average fuel economy stood in President Barack Obama’s first term. Critics objected that low oil prices and the enduring popularity of gasoline-hungry light trucks made those targets hard to reach. So the Obama administration softened the rules a tad, lowering the 2025 standard to 51.4 miles per gallon but keeping the rules essentially intact.

The Energy Information Agency projected last year that the regulations would cut light-duty vehicle gasoline consumption from 8.7 million barrels per day to 7.5 million in 2025, even as car and truck use increased by 5 percent. The Obama administration estimated that consumers would save far more in fuel than it would cost automakers to comply. The standards would substantially reduce the country’s carbon footprint, which is important in persuading other nations to continue cutting their greenhouse emissions, too.

But the industry nevertheless has continued to complain about the standards, which are complex and press automakers to meet the top-line fuel economy targets in specific ways, for example by building more electric cars. Michigan lawmakers have demanded more flexibility in meeting the rules, even as watchdogs have warned that diluting the standards would decrease fuel savings. In other words, there was a reasonable debate to be had about simplifying the regulations.

Instead, the Trump administration is apparently going much further, with some senior officials reportedly considering 2025 fuel-efficiency standards below even the 2018 ones. Cutting the top-line 2025 goal would be a big mistake, and not only for the environment. “We support increasing clean car standards through 2025 and are not asking for a rollback,” Ford Motor Company’s top leaders wrote in a blog post last Tuesday. “We want one set of standards nationally.” Automakers worry that the Trump administration will radically deregulate while a slew of states representing about 35 percent of the nation’s auto market will keep stricter rules. A quirk in the Clean Air Act allows California to set its own car emissions standards, which other states can then adopt, regardless of federal policy, and California is not backing off the Obama-era rules.

Scott Pruitt, the fox-in-henhouse administrator of the Environmental Protection Agency, might try to rip up the waiver under which California exercises its discretion over vehicle emissions. But that would elicit strong legal challenges. Instead, federal authorities should sit down with automakers and California officials to work out a new deal on vehicle emissions — one that does not substantially undercut the goals already in place.

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