Under the Obama administration's Corporate Average Fuel Economy (CAFE) standards, new cars sold in the US must average about 54 miles per gallon by 2025.
The administration said the freeze would boost US oil consumption by about 500,000 barrels of oil a day by the 2030s, and argued it would prevent up to 1,000 traffic fatalities per year by reducing the price of new vehicles and so prompting people to buy newer, safer vehicles more quickly.
Heidi King, the deputy administrator of the National Highway Transportation Safety Administration, said the administration is excited about the idea of getting more modern cars on the road to replace older, less efficient ones.
The proposal from the U.S. Transportation Department and Environmental Protection Agency would freeze fuel efficiency standards at 2020 levels through 2026, and require dramatically fewer electric vehicles as more people continue to drive gasoline-powered vehicles.
Automakers had long bemoaned the Obama standards as too hard to meet, especially as more consumers choose larger trucks, crossovers and SUVs, which guzzle more gasoline. Under the Trump administration's preferred proposal, that would drop to 29.6 miles per gallon, a reduction in nationwide fuel efficiency of about 21 percent. California's standards are followed by 13 other states. California, 16 states and the District of Columbia have already filed a lawsuit that challenges the plan's scientific underpinnings. And what the Trump administration is doing in trying to roll those back, it's going to cost hundreds of billions of dollars more at the pump.
But critics of the proposal note that the auto industry had a stretch of strong sales from 2010 to 2017, with several years seeing record sales, because consumers want more fuel-efficient vehicles. It might even cause vehicle prices to stop increasing so rapidly.
The Natural Resources Defense Council said the administration is "driving our auto future in reverse".
Trump in March 2017 announced his administration would be reopening a review of the Obama automobile rules that he and some automakers said was unfairly cut short by Obama's EPA.
"The National Auto Dealers Association estimates the federal standards demanded by California will add $3,000 to the cost of new motor vehicles by 2025, potentially pricing millions of low-income households out of the market for new cars", Marlo Lewis, a senior fellow at the Competitive Enterprise Institute (CEI), said in astatement.
The argument may prove a tough sell in court, where attorneys for states and environmental groups will come armed with a wealth of data undermining it. Currently California has a special waiver under the Clean Air Act to enact stricter rules than those at the federal level. An Obama-era analysis found no harm to safety from making cars more efficient.
Pollution from cars, trucks and other on-road vehicles is the California's single-largest source of greenhouse gas emissions, according to state data.