Manufacturers continue to build lighter vehicles with improved structural rigidity and ability to protect the driver and passengers during collisions.
Bumpers evolved as rails or bars to protect the front and rear of the carís body from damage in minor collisions. Over the years, bumpers became stylish and, in some cases, not strong enough to survive minor collisions without expensive repairs. Eventually, government regulations required bumpers designed to withstand low-speed collisions with less damage. Some bumpers can withstand 4-km/h (2.5-mph) collisions with no damage, while others can withstand 8-km/h (5-mph) collisions with no damage.
Modern vehicles feature crumple zones, portions of the automobile designed to absorb forces that otherwise would be transmitted to the passenger compartment. Passenger compartments on many vehicles also have reinforced roll bar structures in the roof, in case the vehicle overturns, and protective beams in the doors to help protect passengers from side impacts.
Seat belt and upper-body restraints that relax to permit comfort but tighten automatically during an impact are now common. Some car models are equipped with shoulder-restraint belts that slide into position automatically when the carís doors close.
An air bag is a high-speed inflation device hidden in the hub of the steering wheel or in the dash on the passengerís side. Some automobiles have side-impact air bags, located in doors or seats. At impact, the bag inflates almost instantaneously. The inflated bag creates a cushion between the occupant and the vehicleís interior. Air bags first appeared in the mid-1970s, available as an optional accessory. Today they are installed on all new passenger cars sold in the United States.
Air bags inflate with great force, which occasionally endangers a child or infant passenger. Some newer automobile models are equipped with switches to disable the passenger-side air bags when a child or infant is traveling in the passenger seat. Automakers continue to research ways to make air-bag systems less dangerous for frail and small passengers, yet effective in collisions.