Washington, D.C. – The all-electric Mitsubishi i-MiEV is the “greenest” car in the U.S., knocking the Honda Civic Natural Gas out of the spot it occupied for eight years, according to the annual report by the American Council for an Energy-Efficient Economy (ACEEE).

Making its model-year 2012 debut on the American market, the i-MiEV earned a score of 58, the highest Green Score awarded since the rankings began in 1998. The Mitsubishi was rated at a combined city and highway fuel economy equivalent of 112 miles per gallon (2.1 L/100 km). “Even taking into account the emissions generated from the electricity used to power the i-MiEV, it still handily outscores other vehicles on the market today,” said lead vehicle analyst Shruti Vadiyanathan.

Despite improved fuel economy this year, the Honda Civic Natural Gas moved to second place, tied with the Nissan Leaf. Rounding out the top six are the Toyota Prius, Honda Insight, and Smart ForTwo.

Hybrids dominated the “Greenest” list, occupying half of all spots, while highly-efficient conventional gasoline vehicles claimed three of the top twelve spots.

“It’s increasingly obvious that automakers are fully invested in providing consumers with the widest possible array of vehicle choices,” Vaidyanathan said. “Earning a spot on the ‘Greenest’ list is proving to be a real challenge for automakers, given the variety of vehicle technologies on the market and the proliferation of highly-efficient conventional vehicles. Just using the latest technology does not guarantee a top spot.” New hybrids from Hyundai, Kia and Infiniti did not break into the top twelve.

The vehicles are analyzed by a “Green Score,” a singular measure that incorporates unhealthy tailpipe emissions, fuel consumption, and emissions of gases that contribute to climate change. Several changes were made to the methodology this year to more accurately estimate vehicles’ environmental impacts, include improved emissions estimates for manufacturing processes, changes reflecting current natural gas extraction practices, and consideration of upcoming shifts in the generation mix for the electricity used to power battery vehicles.

Greener Cars also identifies top models in each vehicle class, with the “Greener Choices” list including trucks and SUVs such as the Chevrolet Equinox, GMC Canyon, Honda Odyssey and Ford F-150 FFV. The “Meanest” list this year included a number of heavier light-duty vehicles that pushed European sports cars out as the highest emitters. Topping the list were the Chevrolet G3500 Express/GMC G3500 Savana cargo vans, Ford E-350 Wagon and Bugatti Veyron.

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