Federal regulators are cracking down on automakers whose mileage claims are apparently inflated from what customers experience when they buy the cars.

Under proposed new regulations, carmakers will have to road test the vehicles to back up their miles per gallon figures instead of basing the numbers on laboratory measurements such as wind tunnel. Following recent instances of inflated fuel-economy claims, the Environmental Protection Agency has proposed new tests.

"Some automakers already do this, but we are establishing a regulatory requirement for all auto makers," said Chris Grundler, director of the EPA's Office of Transportation and Air Quality, as quoted by the Wall Street Journal.

The EPA last made changes to mileage claim tests in 2008, after which new-car window stickers generally matched actual fuel economy.

Ford, Hyundai and Kia have all recently been involved in high-profile cases where fuel economy estimates were found to be inflated.

Last month, the American automaker said that the mileage claims on six cars from the 2013 and 2014 model years were inflated. Ford conducted a real driving test that showed the fuel economy figures were inflated and said affected owners would be compensated with $1,050 for the false advertising.

The misrepresented vehicles were mostly hybrid cars and were all highly-fuel efficient, something that can affect test results.

"It isn't well known, but the EPA doesn't test every new car," WSJ reported. "Most lab testing for fuel economy is performed by auto makers and the data is vetted by the agency."

Using a five-part lab test, the EPA tests just 15 percent of the auto industry's offerings each year due to the number of vehicles on the road. The proposal to require automakers to road test their mileage claims will have to go through a public comment period.

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