The chart below shows AutoEcoRating calculations of total lifecycle environmental impact for the Tesla Roadster, Toyota Prius, Nissan Leaf and Chevrolet Volt. As explained in our “What do the numbers mean?” FAQ, this measure uses tons of carbon dioxide (CO2) as a common denominator, but it’s more than just a carbon footprint because it include other environmental impacts as well.
The resulting total pollution numbers are 5.3 for the Roadster, 5.9 for the Prius, 6.1 for the Leaf, and 7.5 for the Volt. The average compact car, which puts out 10.7 tons per year, is also shown for comparison.
Breaking down the pollution by where it occurs, the top part of each bar gives tailpipe pollution. That’s missing for a “zero emissions vehicle” (ZEV), which has no tailpipe. The middle (brown) section of each bar gives the pollution related to producing the fuel, whether at a refinery that produces gasoline (for a hybrid or ordinary cars) or at an electric power plants for anything that plugs in. The lower part of each bar gives pollution during vehicle manufacturing, which covers building the car and producing its parts such as steel and other materials, including batteries.
These tons of pollution values get converted to AutoEcoRating values (“eRatings”) on a higher-is-better scale that is inversely proportional to the amount of pollution produced. That yields eRatings of 226 for the Tesla Roadster, 205 for the Prius, 195 for the Leaf, and 161 for the Volt. The average compact has an eRating of 112, based on a Bin 5 tailpipe emissions certification and a combined fuel economy of 27 mpg as reported in EPA statistics for MY 2010.
The Volt’s impact estimate is based on an assumption that the EPA-rated 35-mile, all-electric range results in operation that is 58% in electric mode, based on projections from a study of possible PHEV usage patterns by Argonne National Laboratory. The rating range for the Volt is an eRating of 138 if driven only on gasoline (obviously an unlikely situation) to an eRating of 183 if driven only on electricity (which many drivers might well try to do).