Pittsburgh, Pennsylvania – Electric vehicles (EVs) with smaller battery packs are more efficient in reducing societal costs for health care, environmental damages and oil consumption, according to a new study by researchers at Carnegie Mellon University.

Associate professor of engineering Jeremy Michalek and his co-authors report that plug-in vehicles with small battery packs and hybrid electric vehicles (HEVs) that don’t plug in can reduce life cycle effects from air emissions and enhance oil security at low or no additional cost over a lifetime, but plug-in vehicles with larger batteries are more costly and may have higher or lower emissions than HEVs, depending on where and when they are plugged in.

“Current government policy provides larger subsidies for vehicles with larger battery packs, assuming that larger is better,” Michalek said. “While larger battery packs allow plug-in vehicles to drive longer distances on electric power instead of gasoline, they are also expensive and heavy, they are underutilized when the battery capacity is larger than needed for a typical trip, they require more charging infrastructure, and they produce more emissions during manufacturing.”

In the U.S., the American Recovery and Reinvestment Act of 2009 provides up to US$7,500 in tax credits for up to 200,000 plug-in vehicles. “Because vehicles with larger battery packs are more expensive, fewer of them can be subsidized, and that can result in lower total benefits,” Michalek said.

Study co-author Mikhail Chester said that is possible that in the future, plug-in vehicles with large battery packs might offer the largest benefits at competitive costs “if the right factors fall into place, including sufficiently low-cost batteries, high gasoline prices, low-emission electricity and long battery life. But such a future is not certain, and in the near term, HEVs and plug-in vehicles with small battery packs provide more emissions benefits and oil displacement benefits per dollar spent.”

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