The Trump administration is facing a lawsuit challenging its plan to reduce federal fuel economy standards for passenger vehicles, a move that environmental groups say will increase costs for drivers and worsen emissions. On Oct. 2, organizations including the Sierra Club, Environmental Defense Fund, and Center for Biological Diversity filed suit to block the National Highway Traffic Safety Administration’s (NHTSA) proposal to lower the required fleetwide average fuel economy from over 50 miles per gallon by 2031 to just under 35 miles per gallon.

The administration argues that easing the fuel economy targets will lower vehicle costs, making cars more affordable for consumers. U.S. Transportation Secretary Sean Duffy and NHTSA Administrator Jonathan Morrison asserted that the rollback would reduce sticker prices by roughly $1,300, enabling more Americans to purchase newer vehicles equipped with enhanced safety features. Duffy described the rollback as ending “an illegal mandate” that forced higher production of costly electric vehicles, which he said many Americans do not want.

The proposal has received backing from major automakers. The Alliance for Automotive Innovation, representing most U.S. car manufacturers, praised NHTSA for aligning standards with current market conditions and the law, emphasizing the need for greater manufacturing flexibility to meet consumer preferences.

Environmental advocates contend that the rollback is ill-timed, pointing to sustained fuel prices averaging about $4.30 per gallon as of early October. They argue that weakening standards will ultimately result in higher gasoline expenses for drivers. Citing NHTSA’s own internal analysis, critics note that under the proposed standards, drivers could pay an additional $1,624 on fuel over the lifetime of a vehicle compared to the current rules. The agency acknowledged that relaxing efficiency requirements naturally leads to increased fuel consumption and higher costs at the pump.

“This reckless rollback prioritizes Big Oil and automaker profits over American families,” said Katherine Garcia, director of the Sierra Club’s Clean Transportation for All initiative. David Pettit, attorney at the Center for Biological Diversity’s Climate Law Institute, called the timing “the worst possible” amid high gas prices, emphasizing the need for more fuel-efficient options.

The dispute over mileage standards dates back to the Trump administration’s initial efforts in 2017 to rollback Obama-era fuel economy regulations, which targeted nearly 55 miles per gallon by 2025. That standard was reinstated under the Biden administration before being subsequently lowered again by Trump. Each administration’s regulatory adjustments have been finalized through official rulemaking.

Notably, although the proposed 2031 target is roughly 35 mpg, recent data from the Environmental Protection Agency indicates that automakers’ current vehicle fleet averages about 27 mpg, equating to approximately 375 miles per tank on a typical 15-gallon gas tank. A reduction from 50 mpg to 35 mpg would cut travel distance per tank by about 125 miles, underlining critics’ concerns over decreased fuel efficiency.

Proponents of the rollback assert that allowing automakers to produce vehicles that consumers want, without stringent mileage mandates, will foster affordability and safety. Opponents maintain that, with historically high fuel prices, maintaining or strengthening fuel economy standards is critical to reducing consumer costs and environmental impact. The outcome of the lawsuit could shape the availability of fuel-efficient vehicles and the trajectory of U.S. fuel economy policy in the coming years.