For the 8th year, the 2011 Honda Civic GX has claimed top honors as the “greenest” car in the United States, according to the 14th annual ratings for the American Council for an Energy-Efficient Economy (ACEEE).

Some newcomers — including an electric vehicle and a plug-in electric hybrid — did well, while several of the regulars held their ground and other cars, most notably the Chevrolet Volt, fared poorly.

This year’s ratings reveal a face-off among plug-ins, gasoline hybrids, diesels, natural gas vehicles, and improving “conventional” gasoline vehicles. notwithstanding changes to Green Book® rating methods that boost.

The all-electric Nissan Leaf places second, followed by the gasoline-powered Smart Fortwo. Hybrids take the next three spots, followed closely by Ford’s new Fiesta SFE (Super Fuel Economy) and the Chevrolet Cruze Eco.

Also notable on this year’s list is the Hyundai Elantra, with a 4 mile-per-gallon jump in fuel economy over the 2010 model. The Chevy Volt Chevrolet slipped to 12th position and five new models joined the list.

According to ACEEE, “the strong showing of conventional vehicles in the top 12 is a testament to how serious manufacturers have gotten about recasting these vehicles as fuel-sippers with transmission refinements, weight savings, and sophisticated internal combustion engines.

Shruti Vaidyanathan, ACEEE vehicle analyst, said:

“We’re seeing an increasing number of highly efficient gasoline options from both foreign and domestic automakers along with the first electric
vehicles. Ford introduced the Fiesta this year and Chevrolet debuted the Cruze, both of which do exceedingly well in our ratings.

Regarding plug-in vehicles, ACEEE Transportation Director Therese Langer noted: “Vehicles running on electricity emit nothing from the tailpipe, but their ‘upstream’ emissions can be substantial, depending on where they’re charged. As U.S. power generation becomes cleaner, these vehicles’ scores will rise.”

The Green Book methodology update also incorporates emissions associated with battery manufacture and disposal in a manner that reflects material content, drawing from Argonne National Lab’s GREET model.

Hybrids lose points on their Green Scores as a result and this year captured only three of the top 12 spots. Once again diesels fall just short of the Greenest list.

This “Greener Choices” list includes trucks and SUVs such as the Hyundai Tucson, Chevrolet Equinox, GMC Canyon, and the Ford F-150 (FFV). The Honda CR-Z and Hyundai Sonata top their respective classes.

Greenest Vehicles of 2011

1. Honda Civic GX
2. Nissan Leaf
3. Smart ForTwo (Cabriolet/Coupe)
4. Toyota Prius
5. Honda Civic Hybrid
6. Honda Insight
7. Ford Fiesta SFE
8. Chevrolet Cruze
9. Hyundai Elantra
10. Mini Cooper
11. Toyota Yaris
12. Chevrolet Volt

The greenercars.org web site also identifies a selection of top, widely-available models in each vehicle class.

For more details on the greenest cars of the year, visit www.greenercars.org.