The Insurance Institute For Highway Safety rated the Nissan Versa as the best car in the category of smallest vehicles sold in the U.S. -- the mini-cars.

The cars, which have gained popularity for fuel efficiency, were compared for protection in front, side and rear crashes. The Versa was rated a "good" in all three categories. Two cars got good ratings in front and side tests, but not rear.

"People traveling in small, light cars are at a disadvantage, especially when they collide with bigger, heavier vehicles," said Adrian Lund, the president of the IIHS. "The laws of physics dictate this."

The Versa outranked six other cars: the Honda Fit, Mini Cooper, Chevrolet Aveo, Scion xB and Hyundai Accent/Kia Rio. The Toyota Yaris was tested with and without optional side air bags.

In the front test, the Versa's structure held up well, which minimized the intrusion into the space around the driver dummy.

In the side test, the standard curtain-style air bags prevented contact between the striking barrier and the heads of the crash test dummies. Nissan said it's modifying the side air bags in cars built after November 2006 to improve protection in side impact crashes.

The Scion, Yaris without air bag and Accent/Rio tested poor in the side evaluation, while the Fit, Aveo and Accent/Rio tested poor in the rear crash test. The Aveo tested marginal in the side evaluation. Only the Versa tested good -- the top possible rating -- in the rear crash test.

The Accent and Aveo didn't perform well, the testing found, despite having standard side air bags.

The Accent's structural performance in the side test was marginal. Curtain-style air bags in the front and rear seats provided good head protection, but measures recorded elsewhere on the driver dummy indicate a motorist in a similar real-world crash would be likely to suffer internal injuries.

The mini-cars tested weigh about 300 pounds less than a typical small car and about 800 pounds less than a midsize car. Lund said that buying cars for good fuel economy doesn't mean having to buy a mini-car.

"Models including the Honda Civic and Toyota Corolla are bigger than the mini-cars we tested and weigh more, so we would expect better occupant protection in serious crashes," Lund said. "At the same time, these and other small car models get nearly as good fuel economy as mini-cars."