Air bags are one part of a vehicle’s occupant protection system, which also includes the structure of the vehicle and seat belts. Seat belts are the primary restraint for an occupant during a crash, and air bags are intended to supplement this protection. In 1999, NHTSA reported that seat belt use alone (lap and shoulder belts) reduces fatalities by 45 percent in crashes involving an impact to the front of the vehicle, frontal air bags without seat belts reduce fatalities by 14 percent, and the combination of seat belts and air bags reduces fatalities by 50 percent. Between 1986 and April 2001, frontal air bags have saved an estimated 6,856 lives but have caused 175 fatalities that have been confirmed by NHTSA—19 infants in a rear-facing child seat, 85 children (not in a rear- facing child seat), 64 drivers, and 7 adult passengers—in relatively low- speed crashes. NHTSA investigators have found that people who were killed by deploying air bags were typically in close proximity to the air bag in one of two ways: The occupant was thrown forward by events that occurred before the air bag deployed, such as sudden braking immediately before the crash or multiple impacts. This usually occurred because the occupant was unbelted or improperly belted. The occupant’s initial seating position placed them close to the air bag. According to NHTSA, these fatalities included shorter drivers who were belted but had moved the seat forward in order to more easily reach the steering wheel and pedals, infants in rear-facing child seats, and children sitting on the lap of another passenger. The majority of people who were killed by deploying air bags in low-speed crashes were unbelted or improperly restrained, which made them more susceptible to being thrown into the path of the deploying air bag than belted occupants. (See fig. 1.) The reported number of air bag-related fatalities increased from 1 in 1990 to 58 in 1997, as the installation of air bags in vehicles increased. Since 1997, the number of fatalities has decreased; 17 fatalities were reported in 2000. NHTSA attributes the decrease in part to actions that resulted from its November 1996 plan to address the risk of air bag-related fatalities. These actions included a public education effort to persuade people to properly restrain infants and children under 12 in the rear seat and issuing a rule in March 1997 that made it possible for manufacturers to quickly reduce the inflation power in the air bags installed in new vehicles. From model year 1997 through 1998, manufacturers lowered the inflation power by an average of 22 percent in driver-side air bags and 14 percent in passenger-side air bags. NHTSA’s 1996 plan also anticipated the need for long-term technological improvements—advanced air bag systems—to control or prevent deployment of the air bag, as appropriate. In June 1998, the Transportation Equity Act for the 21st Century directed the Secretary of Transportation to issue a rule requiring vehicle manufacturers to install advanced air bag systems. The act specified that these systems should achieve two goals—provide improved protection for occupants of different sizes (belted and unbelted) as well as minimize the risk of injury or death from air bags for infants, young children, and other occupants. On May 12, 2000, NHTSA issued a rule specifying the requirements for such a system. Under the previous requirements, vehicle manufacturers performed tests that involved crashing vehicles into a rigid barrier with crash dummies—belted and unbelted—that represented average-sized males in the driver and passenger seats. To provide improved crash protection for occupants of different sizes, the rule adds new crash tests that simulate different types of crashes and include the use of crash dummies that represent small adults (defined as a 5th percentile female). To reduce the risk of injury or death to children and small adults, the rule requires a new battery of “static” tests using dummies representing infants, young children, and 5th percentile females. These tests involve placing the dummy in various positions in the seat to determine if the air bag system suppresses or activates the air bag, or placing the dummy against the air bag module and deploying the air bag to determine if the bag deploys in a “low-risk” manner that does not cause severe injury. Starting in the production year beginning September 1, 2003 (approximately model year 2004) and continuing over a 3-year phase-in period, increasing percentages of each manufacturer’s vehicles must comply with the requirements of the rule. (See app. II for a more comprehensive discussion of the rule’s requirements.) Manufacturers have installed some of the advanced technologies that will be needed to comply with the advanced air bag rule in certain vehicles that are on the market today. (See table 1.) Manufacturers and companies that produce air bags are working on the development of other needed advanced technologies, with the aim of having them ready for installation in vehicles by September 2003, as required. Advanced air bag systems installed in future vehicles will be much more sophisticated than the conventional air bag systems in today’s vehicles, because they will be capable of tailoring air bag deployment to characteristics of the front seat occupants as well as crash severity. Conventional frontal air bag systems deploy the air bags with a single level of inflation output for all crashes that exceed a predetermined severity threshold. These systems generally consist of separate components designed to work together: crash sensors, a control module, and a driver and passenger inflator and air bag. (See fig. 2.) The crash sensors and control module are typically located in one unit within the passenger compartment; the unit is often mounted within the floor between the driver and the passenger. The crash sensors detect the occurrence and severity of crashes and provide this input to the control module. The control module evaluates inputs from the sensors. If the control module determines that a crash has occurred that exceeds the severity threshold, it then sends a triggering signal to the inflators to deploy the air bags. The inflators and air bags are packaged together in air bag modules, which are located in the steering wheel on the driver side and in the instrument panel on the passenger side. Upon receiving a triggering signal from the control module, inflators generate or release gases that rapidly fill the air bags, generally within 1/20 of a second after impact. The purpose of the inflated air bags is to provide protective cushioning between the occupants and the steering wheel, instrument panel, and windshield. However, the “single- stage” inflators in most vehicles today, in some cases, provide more inflation power than necessary because they fill the air bags with one level of output when deployed, regardless of the types of occupants requiring protection or the degree of severity of the crash. Future frontal air bag systems designed to meet the performance requirements of NHTSA’s advanced air bag rule will have additional features that will allow the deployment of the air bags to adapt to characteristics of the front seat occupants as well as different crash situations. Auto manufacturers anticipate that two new components will be needed to meet the rule’s requirements: occupant classification sensors and multistage inflators. Occupant classification sensors will provide an additional input to the control module to detect different types of occupants and whether or not they are belted. For example, manufacturers anticipate installing sensors that will be able to identify whether the front passenger seat is occupied by an infant in a rear-facing child seat, a child, or an adult. Multistage inflators, which will replace single-stage inflators, will provide varying levels of inflation output that can be tailored to characteristics of the driver and front seat passenger as well as different crash scenarios. Deployment options could include no deployment, low-level output, and high-level output, as well as additional levels of deployment between the low- and high-output stages. While the occupant classification sensors and multistage inflators are the key new features of the advanced air bag systems envisioned by auto manufacturers, other components will also be improved. For example, manufacturers anticipate that these systems will include crash sensors that can more precisely discriminate among different types of crashes (such as a crash into a rigid concrete wall versus a crash with another car), control modules that can process the additional inputs provided by crash and occupant sensors and make more accurate and timely deployment decisions, and air bag designs that will allow the bag to deploy less aggressively. These advanced air bag systems will be designed to reduce the likelihood of the types of fatalities previously caused by air bag deployments. For example, such systems would deactivate the passenger air bag or deploy it at a low level if the passenger seat is occupied by an infant or small child.These systems may also adjust air bag deployment if the driver or passenger is a small adult. Some vehicles on the U.S. market today have frontal air bag systems with multistage inflators and some other advanced features, such as seat belt usage sensors and improved air bag designs. However, no vehicles currently on the market have air bag systems with all the features manufacturers believe are needed to fulfill the requirements of the advanced air bag rule. In particular, no vehicles currently have frontal air bag systems with occupant classification sensors that can distinguish among child seats, children, or adults. Manufacturers are not required to produce vehicles that can meet the requirements of the advanced air bag rule until the production year starting in September 2003 (approximately model year 2004). Frontal air bag systems with multistage inflators started appearing on the market in some model year 1999 and 2000 vehicles and became more widely available in model year 2001 vehicles. While three of the eight manufacturers we talked to installed multistage air bag systems in some or all of their model year 1999 vehicles, seven of the manufacturers installed this technology in some or all of their model year 2001 vehicles. Four of these seven manufacturers—BMW, DaimlerChrysler, Ford, and Honda— installed multistage air bag systems in at least one-quarter of their model year 2001 fleets.