Four major automakers on Thursday announced they had reached a deal with California to produce more fuel-efficient cars for the US market, an end run around the Trump administration which is seeking to freeze mileage standards.
California negotiated the agreement with Ford, Honda, Volkswagen and BMW in secret, and said it provided a 50-state solution that would avoid a patchwork of regulations from arising across the country.
Last year, President Donald Trump's administration proposed a rule to axe tougher mileage and greenhouse gas emissions requirements for light-duty cars enacted by his predecessor Barack Obama.
But California, which exercises considerable clout in the auto industry as the country's wealthiest state, announced its intention to set its own regulations.
"These terms will provide regulatory stability, preserve vehicle affordability for customers, reduce compliance costs and result in increased environmental benefits," the manufacturers said in a statement.
The agreement envisages reducing greenhouse gas emissions by 3.7 percent each year from 2022 through 2026.
According to The Washington Post, by 2026, new models would meet a standard of 50 miles per gallon (4.7 liters per 100 kilometers), against the 37 mpg current level -- just one year later than the target set under the Obama administration.
"This is an important breakthrough that will ensure the United States continues to make progress in addressing what is now our largest source of global warming pollution," said Dan Lashof, US director of the World Resources Institute.
"It demonstrates beyond any doubt the recklessness of the Trump administration's efforts to push the nation backwards on climate, regardless of how it harms families or businesses.
"The standards agreed to will save consumers money at the pump, cut air pollution and enable American automakers to better compete in a global market that is gravitating towards less polluting, more efficient vehicles."