The Trump administration's proposal would freeze fuel-efficiency standards at 2020 levels - about 37 miles per gallon by 2026, down from the Obama administration's almost 47 mpg - and weaken electric vehicle mandates.
"We are going to remain committed to improving fuel economy, reducing emissions and working toward an all-electric future, but we believe it is in everybody's best interest to have one national set of requirement that comprehends the new technologies", she said.
California has a lot riding on the lawsuit as the government is also seeking to eliminate the state's ability to set its own vehicle standards. At the moment, the state standard and the national one are the same-but if they diverged, automakers could end up making multiple versions of each auto to sell in different parts of the U.S. The Trump administration wants to take away California's right to set higher standards. The Obama-era standard mandated that automobiles sold by auto companies have to reach 50 miles per gallon (MPG) by 2025.
The Environmental Protection Agency and the Department of Transportation said the increase in emission standards for cars built from 2021 to 2026 would hurt vehicle sales and improve safety of motorists across the country.
The prospect of an extended legal fight has discomfited automakers, who had asked the administration to relax the Obama-era rules but don't want to see the USA market split in two, with different models of cars required in blue and red states.
California is fighting to keep fuel-efficiency standards in place after the EPA announced the rollback of Obama-era mileage standards. It claims that automakers will save billions of dollars in regulatory-related costs, such as developing more efficient vehicles.
"Our latest report completely refutes the administration's flat-out wrong rationale for rolling back the standards", Gillis said.
Pollution from cars, trucks and other on-road vehicles is the California's single-largest source of greenhouse gas emissions, according to state data.
"My job as the state's attorney general is to protect my state's rights and interests and the environmental rights of all Pennsylvanians", Shapiro said.
The Trump administration proposal could also invalidate California's mandate that automakers sell a certain number of electric vehicles. He added "The California Department of Justice will use every legal tool at its disposal to defend today's national standards and reaffirm the science behind them".
"The administration's proposal goes beyond a simple rollback".
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.
Jeff Alson, a former policy adviser for the EPA office of transportation and air quality in Ann Arbor, has worked on vehicle emissions for 40 years at the agency. Letting one state make decisions for people in other states makes a bad program even worse, especially since the state is California, which has been pursuing an anti-car agenda for decades. Despite the waiver, California still fails to meet federal clean air guidelines, the agencies noted.
Now they're only about one-third, with less-efficient trucks and SUVS making up the rest.