The E.P.A. cannot mandate that carmakers sell a certain number of electric vehicles. But under the Clean Air Act, the agency can limit the pollution generated by the total number of cars each manufacturer sells. And the agency can set that limit so tightly that the only way manufacturers can comply is to sell a certain percentage of zero emissions vehicles. The proposed tailpipe pollution limits for cars, are designed to ensure that 67 percent of sales of new light-duty passenger vehicles, from sedans to pickup trucks, will be all-electric by 2032. Additionally, 46 percent of sales of new medium-duty trucks, such as delivery vans, will be all-electric or of some other form of zero-emissions technology by the same year, according to the plan.