Looking back on the green leaders of 2012

Last year, we pitted some of the greenest 2011 models against each other to see which car was the greenest of them all.  This year that crown goes to the Toyota Prius. With the previous leader, the Tesla Roadster, no longer on the market, Tesla now comes in third with its new Model S.

Just like it doesn’t take a weatherman to know which way the wind blows, it doesn’t take our number crunching to know that very small electric vehicles (EVs) will out-green just about everything on motorized wheels other than a Segway and all-electric motorbikes (or perhaps some motorcycles, though those with tailpipes are not as clean on smog as the cleanest cars). So we handicap this list by looking only at vehicles that are at least classified as compacts in terms of size.

The accompanying chart shows how this year’s leading green contenders rank according to their total pollution, with an average compact shown for comparison. Coincidentally, the average 2012 compact car tallies up just about exactly 10 tons of total pollution according to AutoEcoRating analysis, so that’s a handy point of reference for comparing the recent year’s cars.

Leading green vehicles of 2012 ranked by total tons of pollution per year emitted during service

For model year 2012, the Toyota Prius again edges out the Nissan Leaf, leading this group in overall cleanliness. With a super-clean burning, Partial Zero Emission Vehicle (PZEV) certified 1.8 liter engine, the Prius emits just 4.7 tons of pollution per year, counting both its sliver of smog-forming tailpipe pollution (the pink top part of the bar) plus the pollution from burning and refining its gasoline. That’s less than half the pollution of an average compact and earns the Prius — which actually falls into the midsize car class — an eRating of 244.

The all-electric Nissan Leaf has no tailpipe, but the emissions associated with the electric power it consumes plus those associated with the car’s heavier mass (due to its battery) result in a total impact of 4.9 tons of pollution. That gives it an eRating of 233, about 5% below the Prius’s rating but still easily twice as clean as the average compact. Recall that all of our comparisons use national average emissions data. As EV fans well know, electric power generation is much cleaner than average in California and a number of other states, and so in those locales the Leaf outshines the Prius.

New in 2012, the Tesla Model S is an all-electric, four-door sports sedan. Designed with plenty of wheel-spinning electrodrive torque, the Model S claims a 5.6 second zero-to-60 time and earns an eRating of 199. That’s based on its 5.8 tons of overall pollution (again, using the U.S. average electric grid).

Part of what puts the speedy Model S in third place on our chart is its 4647 pound mass. A good bit of this scale-tipping weight comes from the 85 kWh battery tucked beneath the floorboards. Holding more than three times as much energy as the Nissan Leaf’s 24 kWh battery, that’s what gives the Tesla Model S its impressive 265 mile driving range and rubber-burning acceleration. However, the massive battery means greater environmental impacts during manufacturing, an effect that can be seen in how the Model S has the largest green (bottom) portion of the bars shown in our chart.

Rounding out this list of green leaders is the Chevy Volt plug-in hybrid from General Motors. We rate it based on its EPA-calculated all-electric range and a corresponding Society of Automotive Engineers (SAE) standard estimate of the gas-versus-electric fuel mix. On that basis, the Volt emits 6.6 tons of pollution and earns an eRating of  173. Clearly, if you drive a Volt almost always on electricity and charge it in a state with a cleaner-than-average power grid, you’ll get even greener performance than that.


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