Although vehicles in general are much safer in collisions than they used to be, about 30,000 people traveling in passenger vehicles still die in crashes every year. Many factors contribute to fatal crashes, including safety-belt use, driving behavior, road conditions, and a vehicle's crash-avoidance capabilities. But the actual vehicle you're in when a crash does occur can make a life-or-death difference.

Crash tests provide vital insight into the protection offered by different vehicles, and the published scores encourage automakers to make ongoing improvements. But with two primary testing organizations (government and insurance industry) and significant feature variance among cars, it can be difficult to sort through the myriad ratings and manufacturer claims. This crash-test primer will enable you to understand the information that matters and to make an informed decision about your next car purchase.

Structural design and safety systems determine how well a vehicle protects its occupants, but it is independent crash testing under laboratory conditions that measures how well the key components work. A test may reduce the vehicle to a shattered wreck, yet good structural design manages crash forces in such a way that the passenger compartment remains intact and keeps intrusion to a minimum. To protect passengers, important safety systems such as safety belts, air bags, and head restraints mitigate the harsh physical effects of a collision.

The two independent crash-test information sources are the National Highway Traffic Safety Administration (NHTSA) www.nhtsa.dot.gov, a branch of the Transportation Department, and the Insurance Institute for Highway Safety (IIHS) www.hwysafety.org, a safety-research group sponsored by the insurance industry. Using different methodologies, both organizations conduct front and side-impact crash tests. NHTSA also tests for rollover propensity and the IIHS evaluates rear-crash protection.

See videos of how cars perform in IIHS' front and side crash tests.