The plan, developed by the U.S. Environmental Protection Agency and the National Highway Traffic Safety Administration, asserts that lower fuel economy standards will save lives - the higher price of more fuel-efficient vehicles (about $2,300 more per auto, they say) encourages some people to continue driving older, less-safe vehicles, the agencies say.
Easing requirements that cars be more fuel efficient should make them both cheaper and safer, getting vehicles with the latest safety developments in the hands of consumers, officials said.
As vehicle manufacturers boosted fuel economy across their fleets, incremental improvements have become more costly and complicated while returns have diminished, the agencies say.
Thursday's rule-making proposal from the EPA and NHTSA also presents several other options for modifying the Obama targets, while recommending the proposed freeze starting in 2020, the most severe of the scenarios.
"The joint proposal initiates a process to establish a new 50-state fuel economy and tailpipe carbon dioxide emissions standard for passenger cars and light trucks covering MY 2021 through 2026", said the Department of Transportation.
"More realistic standards will promote a healthy economy by bringing newer, safer, cleaner and more fuel-efficient vehicles to USA roads", said Transportation Secretary Elaine Chao. But Trump's EPA said the efficiency rules drive up vehicle prices, keeping many people in older, less safe cars and trucks.
The administration also wants to revoke the authority of California and other states to set their own, stricter mileage standards - independent of federal ones.
"Our proposal aims to strike the right regulatory balance based on the most recent information and create a 50-state solution that will enable more Americans to afford newer, safer vehicles that pollute less", acting EPA Administrator Andrew Wheeler said Thursday. But now, the state's emissions standards are in jeopardy.More news: Trump team wants to roll back Obama-era mileage standards
But consumer advocacy groups, environmental groups and medical associations have said the rule would hurt Americans by costing them more at the pump and releasing more air pollution in the long run.
"Everyone loses at the end", says Simon Mui, a senior scientist at the environmental nonprofit NRDC and the California lead for the organizations' clean vehicles and fuels, climate, and energy program. Twelve other states have adopted those tougher rules, representing about 40 percent of the country's auto market.
"If the standards threatened auto jobs, then common-sense changes could have and should have been made".
Sen. Kamala Harris (D-Calif.) tweeted soon after the White House announced the policy change that she saw this as proof that the Trump administration was prioritizing "lining the pockets of big oil over protecting our right to breathe clean air".
Longstanding federal legislation has allowed California to set its own mileage standards given the choking smog that still sometimes blankets Los Angeles and other central and Southern California valley cities. "From a consumer angle, from an environmental angle, from an industry angle, there's just no great logic [for this proposal] outside of the administration really catering to extremist viewpoints".
The administration also proposed a withdrawal of California's Clean Air Act preemption waiver.
The rollback would undermine efforts by California and several other states to meet commitments the US made in the Paris agreement on climate change.