The battery-powered Nissan Leaf and Chevrolet Volt extended-range electric car have each earned a “Top Safety Pick” award from the influential Insurance Institute of Highway Safety. It is the first time that mainstream plug-in vehicles have been evaluated by the organization.

Both cars received the Institute’s highest score of “good” for front, side, rear and rollover protection and come equipped with electronic stability control, a requirement for the “Top Safety Pick” designation.

“The way an electric or hybrid model earns top crash test ratings is the same way any other car does,” says IIHS Chief Administration Officer Joe Nolan. “Its structure must manage crush damage so the occupant compartment stays intact and the safety belts and airbags keep people from hitting hard surfaces in and out of the vehicle.”

The 2011 Nissan Leaf is a pure electric vehicle with an EPA rated range of 73 miles per charge. The 2011 Chevrolet Volt operates as an electric car for 35 miles then engages a traditional internal combustion engine to generate electricity and provide some drive assistance to the wheels.

The IIHS notes that the added weight of the vehicles’ large battery packs also contributes to their overall safety, as they are much heavier than cars of similar size. For instance, at 3,781 pounds, the compact Volt hatchback weighs more than the full-size Chevy Impala sedan. Experts generally agree that heavier vehicles are safer in car-to-car collisions.

While the integrity of the lithium-ion batteries themselves wasn’t the focus of the tests, the IIHS found that the installation of the packs near the center of the vehicles insulated them from any impact damage. Combined with automatic cut-off systems that activate in the event of collision, this prevented the batteries from transferring electricity to parts of the vehicles that a passenger – or the IIHS testing staff – might come in contact with.

Through March of this year, Chevrolet had sold over 1,500 Volts, while Nissan delivered nearly 500 Leafs. Both automakers have said that they plan to deliver approximately 10,000 of each model in the United States by the end of 2011 and expect to ramp up production significantly next year. However, Nissan’s outlook has been hindered somewhat by the recent natural disasters in Japan.

Neither car has yet been evaluated under the National Highway and Transportation Safety Administration’s Five-Star crash testing procedure, another highly-touted safety benchmark for the industry. Both ratings are considered to be important marketing tools for car companies, particularly for vehicles that use new or alternative technologies that are of concern to some consumers.

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