The EPA is considering regulations that would require automakers to track-test vehicles in order to validate fuel economy claims.

"EPA fuel economy labels are based on sophisticated laboratory testing, which allows precise control of many important variables that can affect fuel economy, and which yields data that are consistent, accurate, and repeatable in a way that real world driving can never be," said An EPA spokeswoman to Edmunds.

As many drivers have found however, mileage could vary.

The current EPA testing formula, which was implemented in 2008, helped reduce the difference between the mileage printed on window stickers and real-world consumer experience.

 In some cases mileage claims, especially for hybrid vehicles, were reduced by as much as 30 percent.

Proposed changes to the EPA requirements, which the spokeswoman said are "still in the consideration phase," would bring manufacturer claims closer in line with what consumers are actually experiencing.

"EPA is considering requiring automakers to perform supplemental test-track audits of production vehicles to validate the values for aerodynamic drag and tire friction, which are important data inputs for our laboratory fuel economy testing. Augmenting EPA's existing pre-production procedures with post-production audits of real-world factors will help further ensure that the data used in EPA labels accurately reflect the vehicles consumers find on dealer lots," said the spokeswoman.

Previously, the EPA required Ford to correct fuel economy labels on vehicles like the 2013-'14 Ford Fusion Hybrid and Energi vehicles and the Ford C-Max Hybrid and Energi models when they were found to have hopeful window stickers.

Kia and Hyundai confirmed in 2013 that they have to pay up to $395 million to settle consumer lawsuits due to overstated fuel economy ratings in the U.S.

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