Inside a secretive government laboratory, behind a tall fence and armed guards, a team of engineers has been dissecting the innards of the newest all-electric vehicles with a singular goal: Rewrite tailpipe pollution rules to speed up the nation’s transition to electric cars.

On Wednesday, the Environmental Protection Agency is expected to propose ambitious greenhouse gas emission standards for cars that are so stringent, they’re designed to ensure that two-thirds of the new vehicles sold in the United States are all-electric by 2032, up from just 5.8 percent today. And the rules could put the nation on track to end sales of new gasoline-powered cars as soon as 2035.

Transportation is the largest source of the greenhouse gases generated by the United States and scientists say that slashing pollution from tailpipes — fast — is essential to averting the most catastrophic impacts of global warming.