Today's air bag requirements evolved over a 25-year period. NHTSA issued its first public notice concerning air bags in the late 1960's. Although vehicle manufacturers began installing air bags in 1986, it was not until the fall of 1996 that manufacturers were first required to install air bags in any motor vehicles.(14)
When the requirements for automatic protection (i.e., protection by means that require no action by the occupant) were adopted in 1984 for passenger cars, they were expressed in broad performance terms that provided vehicle manufacturers with choices of a variety of methods of providing automatic protection, including automatic belts and air bags. Further, the requirements gave vehicle manufacturers broad flexibility in selecting the performance characteristics of air bags. Later, those requirements were extended to light trucks. While vehicle manufacturers initially installed automatic belts in many of their vehicles, ultimately, strong market preference for air bags led manufacturers to move toward installing them in all of their passenger cars and light trucks.
In 1991, Congress included a provision in ISTEA directing NHTSA to amend Standard No. 208 to require that all passenger cars and light trucks provide automatic protection by means of air bags. ISTEA required at least 95 percent of each manufacturer's passenger cars manufactured on or after September 1, 1996, and before September 1, 1997, to be equipped with an air bag and a manual lap/shoulder belt at both the driver and right front passenger seating positions. Every passenger car manufactured on or after September 1, 1997, must be so equipped. The same basic requirements were phased in for light trucks one year later.(15) The final rule implementing this provision of ISTEA was published in the Federal Register (58 FR 46551) on September 2, 1993.
Standard No. 208's automatic protection requirements are performance requirements. The standard does not specify the design of an air bag. Instead, when tested under specified test conditions, vehicles must meet specified limits for injury criteria, including criteria for the head, chest and thighs, measured on 50th percentile male test dummies. Until recently, these criteria limits had to be met for air bag-equipped vehicles in barrier crashes at speeds up to 48 km/h (30 mph), both with the dummies belted and with them unbelted.
However, on March 19, 1997, the agency published a final rule temporarily amending Standard No. 208 to provide the option of testing air bag performance with an unbelted dummy in a sled test incorporating a 125 millisecond standardized crash pulse instead of in a vehicle-to-barrier crash test. This amendment was made primarily to expedite manufacturer efforts to reduce the force of air bags as they deploy.
Standard No. 208's current automatic protection requirements, like those established 14 years ago in 1984, apply to the performance of the vehicle as a whole, and not to the air bag as a separate item of motor vehicle equipment. The broad vehicle performance requirements permit vehicle manufacturers to "tune" the performance of the air bag to the specific attributes of each of their vehicles.
The Standard's requirements also permit manufacturers to design seat belts and air bags to work together. Before air bags, seat belts had to do all the work of restraining an occupant and reducing the likelihood that the occupant will strike the interior of the vehicle in a frontal crash. Another consequence of not having air bags was that vehicle manufacturers had to use relatively rigid and unyielding seat belts that can concentrate a lot of force along a narrow portion of the belted occupant's body in a serious crash. This concentration of force created a risk of bone fractures and injury to underlying organs. The presence of an air bag increases the vehicle manufacturer's ability to protect belted occupants. Through using force management devices, such as load limiters, a manufacturer can design seat belts to extend or release additional belt webbing before the belts concentrate too much force on the belted occupant's body. When these new belts stretch or extend, the deployed air bag is there to prevent the belted occupant from striking the vehicle interior.
Further, as noted above, Standard No. 208 permits, but does not require, vehicle manufacturers to design their air bags to minimize the risk of serious injury to unbelted, out-of-position occupants, including children and small drivers. The standard gives the manufacturers significant freedom to select specific attributes to protect all occupants, including attributes such as (1) the crash speeds at which the air bags deploy, (2) the force with which they deploy, (3) air bag tethering and venting to reduce inflation force when a deploying air bag encounters an occupant close to the steering wheel or the instrument panel, (4) the use of sensors to both detect the presence of rear-facing child restraints and the presence of small children and prevent air bag inflation, (5) the use of sensors to detect occupant position and prevent air bag inflation if appropriate, and (6) the use of multi-stage versus single stage inflators. Multi-stage inflators enable air bags to deploy with lower force in low speed crashes, the type of crashes in which children and drivers have been fatally injured, and with more force in higher speed crashes.