President Donald Trump said Saturday he had approved new fuel economy standards for passenger vehicles, a major reversal of Biden-era requirements that had pushed automakers toward more efficient cars and electric vehicles. The revised standards are expected to set an average of about 34.5 miles per gallon for cars and light trucks through model year 2031, nearly one-third below the 50.4 mpg fleetwide average required under the Biden administration’s rules. The final regulation was not available Saturday, and the White House had not responded to questions about it. Trump cast the change as a way to reduce vehicle costs and give automakers more flexibility. In a social media post, he said the previous standards had forced Americans toward unwanted vehicles and burdened manufacturers. Transportation Secretary Sean Duffy said a major victory for auto workers was coming Monday. The announcement comes as the White House faces pressure over U.S. gasoline prices, which averaged just under $4.50 a gallon Saturday, as well as rising car prices and a coming midterm election. But the standards’ practical effect may be limited by a change Congress made last year. The tax and spending law set aside penalties automakers had faced for failing to meet fuel economy averages, leaving companies with less financial pressure to comply. Joshua Linn, a University of Maryland professor and senior fellow at Resources for the Future, said that change made the standards more like a recommendation than a requirement. Without penalties, he said, manufacturers can decide whether to improve efficiency based on their business calculations. The rollback is part of a broader retreat from federal policies supporting cleaner vehicles. The administration moved in February to undo federal vehicle climate rules, including the scientific finding that greenhouse gases endanger public health. Congress also eliminated consumer tax incentives for electric vehicles last year. The new fuel economy regulation is likely to be challenged in court, as the separate reversal of vehicle emissions rules has been. Legal disputes will test the federal government’s authority to require automakers to improve efficiency or invest in electrification. Dan Becker, who directs the Safe Climate Transport Campaign at the Center for Biological Diversity, argued the change could weaken U.S. automakers as global competitors advance electric vehicle technology. The policy shift also widens the gap between U.S. transportation rules and international trends favoring electric vehicles.