Electric cars scored top safety ratings from the Highway Safety Institute this week in its first ever safety test of electric cars.

The Chevy Volt and Nissan Leaf both received top scores for front, side and rear impact crashes.

Both electric cars have large battery packs that make them weigh more than traditional cars.

The Volt, for example, weighs 3,760 pounds, close to the weight of the Chevrolet Impala. The Leaf weighs 3,370 pounds, similar to a Nissan Altima midsize car. That extra mass helps protect their passengers, since heavier cars are less likely to be pushed around in a crash.

The Nissan Leaf runs solely on battery power and can go about 100 miles on a single charge. The Chevy Volt's can achieve a distance of 40 miles on electricity before a small gasoline engine kicks in to power the vehicle.

The institute said it was the first time it has tested road-worthy plug-in cars.

Two golf cart-like electric vehicles, the Gem e2 and Wheego Whip, were tested for research purposes but performed poorly in side-impact tests, the group said. But those cars run at very low speeds and aren't required to meet federal safety standards.

The federal government hasn't yet released crash-test results for the Volt and Leaf.

"What powers the wheels is different, but the level of safety for the Volt and Leaf is as high as any of our other top crash test performers," said Joe Nolan, the institute's chief administrative officer.