Lifecycle CO2 emissions of five different types of vehicles by region. Image credit: CMU College of Engineering.Lifecycle CO2 emissions of five different types of vehicles by region. Image credit: CMU College of Engineering.Where you live plays a large role in determining the size of the carbon footprint of the vehicle you drive, a study by Carnegie Mellon University has found.

“Most electric vehicle buyers assume that they’re helping the environment by purchasing an electric or hybrid vehicle, but there’s more to it than simply making the purchase,” says study co-author Jeremy Michalek, professor of mechanical engineering.

The study is the first to account for the combined regional influence of driving patterns—such as distance and highway vs. city driving—electricity grid emissions and temperature on the lifecycle emissions of five different types of vehicles. The vehicles compared were the Nissan Leaf, the Chevrolet Volt, the Mazda 3 and the Toyota Prius hybrid and plug-in hybrid models.

Comparing the vehicles' emissions, the researchers found that the entirely battery-run 2013 Nissan Leaf produces lower greenhouse gas emissions than the entirely gasoline-run 2013 Toyota Prius in urban areas of Texas, Florida and much of the southwestern United States. But in the rest of the country, most notably in the Midwest and the South, the Leaf emits more greenhouse gases than the Prius.

Current federal policy for plug-in electric vehicles is fairly uniform across the United States, although different states have varying policies to encourage electric vehicle sales, including subsidies and mandates. The study identifies regions where electric vehicles offer the largest reductions of carbon dioxide emission to help inform future regional policy decisions.

“Electric vehicles offer the largest benefits for urban drivers in mild-climate regions with a clean electricity grid, such as San Francisco or Los Angeles,” says Michalek. “In the rural regions of the colder, coal-heavy Midwest, electric vehicles are often higher emitting than comparable gasoline vehicles today.”

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