The Trump administration rolled back Obama-era pollution and fuel efficiency rules for cars and light trucks on Monday, saying they were too stringent.
The decision by President Donald Trump's Environmental Protection Agency means the emission standards for vehicles in the 2022-2025 model years will be revised, as sought by automakers.
"The Obama administration's determination was wrong," said EPA chief Scott Pruitt.
Former President Barack Obama's EPA "made assumptions about the standards that didn't comport with reality, and set the standards too high," Pruitt said in a statement.
The rules set in 2012, known as the Corporate Average Fuel Economy or CAFE standards, sought to reduce pollutants released into the air by gradually increasing fuel efficiency across all models offered by manufacturers to 54.5 miles per gallon (4.32 liters per 100 kilometers) compared to 35.5 miles per gallon in 2016.
Pruitt said the EPA in 2012 cut short its review of the standards for "politically charged expediency," but he will work with the National Highway Traffic Safety Administration to develop new, "more appropriate" rules.
Pruitt said the agency also is looking at the waiver that allows California, the most popular US state, to impose tougher requirements than called for under the Clean Air Act.
One state cannot "dictate standards for the rest of the country," he said, adding: "EPA will set a national standard for greenhouse gas emissions that allows auto manufacturers to make cars that people both want and can afford—while still expanding environmental and safety benefits of newer cars."
This is likely to open a long legal battle between California, a traditionally Democratic state, and Trump's Republican administration.
California Attorney General Xavier Becerra said the EPA's "assault" on CAFE standards "risks our ability to protect our children's health, tackle climate change, and save hardworking Americans money."
"We're ready to file suit if needed to protect these critical standards and to fight the Administration's war on our environment," Becerra said in a statement.
Trump has been scaling back many types of regulations, including environmental standards, put in place by his predecessor, including pulling out of the Paris climate accord.
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