WASHINGTON (Reuters) - The U.S. vehicle fleet hit a record for fuel efficiency in 2018 averaging 25.1 miles per gallon (mpg) in real-world driving as it rose 0.2 mpg, the Environmental Protection Agency (EPA) said.

FILE PHOTO: Lights illuminate the roadway as cars sit in traffic to depart New York City the day before the Thanksgiving holiday in New York, U.S., November 27, 2019. REUTERS/Lucas Jackson

The fleet is also preliminarily anticipated to jump to 25.5 mpg for the 2019 model year.

The EPA and the National Highway Traffic Safety Administration are working to finalize rules to rollback Obama-era requirements through the 2026 model year. Officials hope to finalize the new rules by April 1 but are still working to address remaining issues.

The report also showed Fiat Chrysler Automobiles NV purchased a significant number of vehicle emissions credits, while Tesla Inc, Honda Motor Co and Toyota Motor Corp sold credits. Daimler AG, Volkswagen AG VOWG_p.DE and BMW AG also bought credits.

Among the 13 largest automakers, only VW and Hyundai Motor Co saw average fuel economy fall in 2018, as they sold more SUVs and fewer cars.

Dan Becker, director of the Safe Climate Campaign, said automakers were far short of the 1 mpg improvement they were supposed to meet in 2018. “The rules should be strengthened to cut pollution and save consumers money at the pump,” Becker said.

EPA Administrator Andrew Wheeler cited the small annual increases as evidence the Obama era requirements are “unfeasible.”

A group representing nearly all major automakers said the report “demonstrates the market challenges that exist” and noted most automakers needed to rely on credits to comply with 2018 requirements.

The Trump administration proposed in August 2018 freezing fuel efficiency standards at 2020 levels through 2026, erasing the increases enacted in 2012.

The draft proposal would boost the stringency of U.S. vehicle emission standards by 1.5% annually from the 2021 through 2026 model years, Senator Tom Carper said in January.

Carper said the draft would result in a 40.5 mpg fleet average by 2030. The administration’s 2018 proposal would have resulted in an average fuel efficiency of 37 mpg by 2026, compared with 46.7 mpg under the Obama rules.

The administration argues the rollbacks are necessary for economic and safety reasons, but California and environmentalists reject that, saying consumers would spend hundreds of billions more in fuel costs.

An EPA science advisory board analysis released on Monday found “significant weaknesses in the scientific analysis of the proposed” rollback, adding it leads to “implausible results regarding the overall size of the vehicle fleet” by predicting hiking prices will cause the vehicle fleet to “grow substantially when it would usually be expected to shrink.”

The EPA said that when finalized the “analysis backing the final rulemaking will be publicly available” and the administration will respond to all comments.