The Institute estimates that nearly 10,000 motor vehicle occupant deaths occur each year in side impact crashes, and more than half of these deaths involve head injuries. Head injuries are the cause of death in 51 to 74 percent of single-vehicle side impacts and 41 to 64 percent of multiple-vehicle side impacts. In addition, 38 percent of occupant deaths occur when a pickup or sport utility vehicle hits a car.

Adrian Lund, chief operating officer for the Institute, says that consumers should not buy a vehicle simply because it has a side air bag. There are other factors, such as frontal air bags and head and neck restraints, that contribute to a car's overall safety. "To say that consumers should only consider cars that have side air bags is going too far," he says. "But if any consumer is looking at a new car and their main concern is safety, they should look for side air bags."

If a side air bag is available only as an option, it may cost you between $250 and $400 to have one installed. Lund says that the government is unlikely to make side air bags mandatory in vehicles any time soon because they still pose a danger to shorter occupants, as do frontal air bags.

Chevy pickups and utility poles

In the first set of crash tests, a Chevrolet pickup crashed head first into the side of a Volvo S80. In one test, the Volvo S80 contained a side air bag. In the other test, it did not.

In the test without the air bag, the heads of the driver and rear passenger dummies were struck by the hood of the pickup truck, and the rear passenger dummy hit the pickup truck hood with such force to cause a fatal head injury. In the test with the air bag, both dummies recorded low head forces because the air bag provided a cushion between the dummies' heads and the hood of the pickup truck.

The Institute also performed crash tests in which a Volvo S80 and a BMW X5 each driving 18 miles per hour crashed sideways into a utility pole. The Volvo S80 had an inflatable curtain, while the BMW X5 had a tube-shaped air bag. The tests reported "major penetration into the side of each car. Yet the forces recorded on the dummies' heads in these tests were low," according to the Institute.