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The agency thinks the new approach will result in more realistic ratings, especially for hybrids.

The Environmental Protection Agency is getting tired of discovering automakers overstating their vehicles' fuel economy figures, and it's apparently actually trying to do something about it. The government regulator has issued a new proposal that would force companies to conduct road tests to calculate their figures. The regulation isn't a guarantee yet, though, because it first has to go through a period of public comment.

According to The Wall Street Journal, the proposed rules come partially as a result of Ford, Hyundai and Kia re-stating the fuel economy results of select vehicles after finding their original ratings to be inaccurate. Under the regulation, automakers would be required to create their calculations for air resistance and rolling friction from real-world data gathered on a test track, rather than from computer models. Currently, EPA test procedures take place on dynamometers and involve professional drivers executing standardized tests designed to mimic typical city and highway drives.

The agency thinks that the new approach will result in more realistic ratings, especially for hybrids. "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 WSJ.

Ford faced a very similar problem with bad data in June when it re-rated the fuel economy of several – predominately hybrid – models downward. The company was using a metric called Total Road Load Horsepower that was a measure of resistance on the dynamometer during testing. However, for these vehicles, the TRLH value proved inaccurate and threw off the mpg numbers.

The EPA wasn't happy about the change. "This issue highlights the need for continued strong oversight of the fuel economy labeling program," said a statement from Grundler after Ford's announcement. "Consumers need to trust that fuel economy window stickers are giving consumers reliable and fair estimates of real world fuel economy."

There may also be good news for the fuel economy ratings of diesel vehicles in the future. According to the WSJ, Grundler is also tasking engineers to find out why the EPA's tests tend to rate diesels lower than their real-world results.

Do you think real-world fuel economy road tests are a good idea, or will they just lead to more variation? Vote in our poll below, then have your say in Comments.

Should the EPA's fuel economy test procedures include real-world road testing?
Yes, absolutely.8746 (94.2%)
No, absolutely not.346 (3.7%)
I'm not sure.189 (2.0%)