Recent incidents of carmakers overestimating fuel economy have led the U.S. Environmental Protection Agency (EPA) to consider stricter testing standards.
But the unfolding Volkswagen diesel emissions scandal may finally be pushing the agency to take concrete action.
Last week, EPA chief Gina McCarthy said the agency would implement measures to prevent cheating on emissions tests, As VW did with software hidden in 482,000 TDI diesel models in the U.S.
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The software allowed cars to detect the conditions of a laboratory emissions test, but the EPA may add on-road testing to its regimen, Chris Grundler--head of the agency's Office of Transportation and Air Quality--told the Associated Press.
While on-road testing is not required under current regulations, Grundler says the EPA does have the equipment needed to conduct it.
However, he said this equipment has been used only to monitor fuel economy and emissions of gasoline passenger cars and diesel heavy-duty trucks--segments where disparities have been uncovered before.
2014 Volkswagen Jetta SportWagen
The EPA has limited resources for testing fuel economy and emissions, which is why it did not originally discover that Volkswagen was cheating.
Since the agency cannot test every new car, automakers generally test cars themselves and submit the results. A portion of these results are audited by the EPA.
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Cars are tested on dynamometers in a laboratory setting, under parameters set by the EPA.
The software installed on certain VW and Audi diesel cars beginning with the 2009 model year could apparently detect the conditions of a laboratory test, and alter an engine's behavior to reduce emissions.
Independent researchers from West Virginia University, working with the International Council on Clean Transportation (ICCT), initially uncovered VW's ruse, using on-road testing.
2015 Volkswagen Golf TDI
Over the past few years, Ford has been forced to lower fuel-economy ratings twice, and Hyundai and Kia were also found to be overestimating gas mileage.
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This led the EPA to issue new testing guidelines in February, hoping to eliminate any discrepancies in how cars are prepared for testing.
These guidelines are not legally binding, but officials felt it would be better to issue them in a timely manner than engage in the drawn-out process of drafting full regulations.