The Environmental Protection Agency wants auto makers to road test the mileage claims they submit after a rash of recent inflated fuel-economy claims based on wind tunnel and other laboratory measurements.

The proposal, which would require a public comment period, comes after several high profile cases in which estimates provided by Ford Motor Co., Hyundai Motor Co. and Kia Motors Corp. were inflated and triggered complaints to regulators and auto makers. The EPA has adjusted the test over the years—most recently in 2008—to...