Have you, or has anyone you know ever bought a car hoping to enjoy high mpg claims and then had a hard time meeting the exalted numbers?

If a U.S. Environmental Protection Agency proposal has its way, this may become less likely as it will require automakers to road test and prove their presently self-certified ratings to the EPA.

As things are now, lab and simulated driving tests – last updated and made more realistic in 2008 – are how it’s done, and we’ve seen in recent weeks Ford (again) add its name to those who’ve needed to revise stated estimates.

The proposed EPA rule would require real-world tests to account for air resistance, rolling friction on a test track instead of lab tests.

“Some automakers already do this, but we are establishing a regulatory requirement for all automakers,” said Chris Grundler, director of the EPA’s Office of Transportation and Air Quality, to the Wall Street Journal.

The move follows an admittance by Ford, which last year came clean saying it never actually tested the C-Max as it lowered its mpg rating, and this year again when it said its C-Max needed to be lowered yet more, along with other cars.

Hyundai and Kia also in 2012 apologized for mis-stating claims and boh it and Ford have had to compensate owners.

If ever there were a case of “over promising and under-delivering” by deliberate fudging of mpg results, this certainly is one case where it is most inadvisable.

The EPA’s move is part of a broader effort to more closely examine automakers’ claims.

The most common complaint by consumers is inability to meet rated mpg figures, and hybrid vehicles particularly can see a swing from as-stated or better, to far less, depending on driving conditons.

Automotive News