In the Cobalt, forces on the driver dummy's torso indicated the possibility of rib fractures or internal organ injuries. In the Corolla, there was the possibility of a fractured pelvis. Protection for the rear passenger was good in both cars.

Another 12 small cars earned poor ratings: Dodge Neon, Ford Focus, Hyundai Elantra, Kia Spectra, Mazda 3, Mitsubishi Lancer, Nissan Sentra, Saturn ION (tested with and without side air bags), Suzuki Forenza, Suzuki Aerio, and Volkswagen New Beetle. Three more small cars will be tested in side impacts later this year. The Mini Cooper and Subaru Impreza will have new design features that are intended to improve side impact protection. The Honda Civic will be a completely redesigned model.

In the side-impact test, a moving deformable barrier strikes the driver side of a passenger vehicle at 31 mph. The barrier weighs 3,300 pounds and has a front end shaped to simulate the front end of a typical pickup or SUV. Each side-struck vehicle contains two instrumented dummies the size of a small woman, one positioned in the driver seat and one in the rear seat behind the driver.

The worst performer was the Neon, according to Lund. “This car is a disaster,” he said. “The structure is poor, and both dummies' heads were hit by the barrier during the crash test. High forces were recorded on the head, torso, and pelvis of the driver dummy. If this had been a real driver in a real crash, it's likely that it would not have been survivable.”

Vehicles need good structure, as well as side air bags, Lund noted. Four of the vehicles that earned poor ratings (Elantra, Forenza, New Beetle, and Spectra) were equipped with standard side air bags with head protection. These cars were rated good or acceptable for head injury measures recorded on the driver dummies. The Saturn ION with optional side air bags also earned an acceptable rating for driver head injury. However, the structures of all of these vehicles allowed too much intrusion during the test. Forces recorded on the driver dummies' torsos and pelvic areas were high.

“Side air bags can protect the head, but if the vehicle structure doesn't hold up well, serious injuries to other body regions still can occur,” Lund said. “With better structures along with the side air bags, the performances of these vehicles would improve.”

Side air bags with head protection are reducing deaths by about 45 percent among drivers of cars struck on the driver's side, according to IIHS research. Before the availability of head-protecting air bags, virtually nothing prevented people's heads from being struck by intruding vehicles or rigid objects, such as trees or poles. Side air bags that protect the chest and abdomen, but not the head, also have reduced deaths by about 10 percent. Well designed doors with appropriate padding are additional protection for the chest and abdomen.