Here’s some good news for all those who are environmentally conscious and want to drive the greenest car possible. The American Council for an Energy-Efficient Economy (ACEEE), a nonprofit organization dedicated to advancing energy efficiency to protect the environment and strengthen the economy, has announced its list of 12 vehicles of 2009 that make the least environmental impact.

Going by the list, you need to either get a car that’s smaller in size or that’s fitted with a hybrid powertrain in order to become environmentally friendly on the road. The ACEEE’s “2009 Green Book” has listed out four hybrids among the top 12 green vehicles sold in the U.S.

The Green Book is an annual guide that evaluates the environmental impact of vehicles available in the new model year and allots them a Green Score based on the impact (from least to worst). The Green Score is determined by various factors such as fuel economy, tailpipe and other emissions that can cause global warming. The higher the Green Score, the lower is the environmental impact.

Rankings

The natural-gas-powered Honda Civic GX has topped ACEEE’s list of “Greenest Vehicles” for the third consecutive year. The Civic GX runs on compressed natural gas (CNG) and is the only vehicle in the list that does not operate on gasoline. It gets a Green Score of 57 for its combination of high efficiency and near-zero emissions that makes it the cleanest car on the road today.

Hybrids - the Toyota Prius, Honda Civic and Toyota Camry Hybrid have gained the second, third and twelfth slots respectively, on ACEEE’s list of eco-friendly vehicles. The other hybrid that has made it into the top 12 happens out to be the largest car on the list as well: the Nissan Altima Hybrid. These hybrids combine an internal-combustion engine with an electric motor for enhanced fuel economy and low emissions.

Two domestic vehicles - the Chevrolet Cobalt XFE (and its Pontiac G5 twin) and the Chevy Aveo/Aveo5 have received eighth and 10th rankings respectively. Meanwhile, the two European brands that made it to last year’s list, have again found a place in the list. The MINI Cooper/Clubman is ranked seventh with a green rating of 45, while the Smart Fortwo which is the smallest car on the list, gets fourth position with a green score of 49.