Fatality Reduction by Air Bags:
Analyses of Accident Data Through Early 1996

Charles J. Kahane, Ph.D.

The fatality risk of front-seat occupants of passenger cars and light trucks equipped with air bags is compared to the corresponding risk in similar vehicles without air bags, based on statistical analyses of Fatal Accident Reporting System (FARS) data from 1986 through early 1996. The principal conclusion is that driver air bags save lives. The fatality reduction benefit of air bags for all drivers is an estimated 11 percent; this percentage is essentially unchanged from 1992 and 1994 analyses by NHTSA staff. New, positive findings are that driver air bags save lives in light trucks and in small cars, that passenger air bags save lives of right-front passengers age 13 or older, and that driver air bags provide a significant supplemental life-saving benefit for the driver who buckles up (as well as saving lives of unbelted drivers). On the other hand, preliminary analyses of limited accident data show a higher fatality risk for child passengers age 0-12 in cars with current dual air bags than in cars without a passenger air bag. Also, current air bags may have diminished, or even negligible benefits for drivers age 70 or older, and they do not have a statistically significant effect for drivers of any age group in oblique-frontal crashes.

Executive Summary

Driver air bags first appeared as standard equipment on a few 1985 make-models. When automatic occupant protection was phased into passenger cars during model years 1987-90, the National Highway Traffic Safety Administration (NHTSA) did not mandate air bags, but allowed any system meeting the agency's test requirements, such as air bags or automatic belts. Nevertheless, the agency explained that the combination of a 3-point safety belt, correctly buckled, plus an air bag provides the best occupant protection. The public agreed, expressing an almost immediate preference for air bags over automatic belts. In 1990, more than a million cars with driver air bags were sold. By 1993, the majority of new cars had driver air bags, and by 1994, dual air bags. By 1995, the majority of new light trucks had driver or dual air bags. All new cars will be required to have dual air bags and manual 3-point belts in model year 1998, and all new light trucks in 1999.

Pursuant to Executive Order 12866, NHTSA evaluates the actual safety benefits of its existing regulations, based on statistical analyses of accident data, to see if the standards are indeed effective and meeting their regulatory goals. The fatality-reducing effectiveness of air bags is a matter of continuing interest to NHTSA. Statistical analyses of the available accident data were published in 1992 and 1994. The 1992 analysis found that air bags for drivers of passenger cars were reducing fatality risk by 11 percent; the 1994 analysis found a 10 percent reduction. NHTSA now has records of 7933 driver fatalities in cars equipped with air bags, as compared to 777 at the time of the 1992 study and 2069 in 1994. A more detailed analysis of fatality reduction can be performed for car drivers. Also, since there have been 855 driver fatalities in light trucks and vans equipped with air bags and 782 right-front passenger fatalities in cars equipped with dual air bags, it is possible to take a first look at the effect of air bags for drivers of light trucks and for car passengers.

Analyses are based on Fatal Accident Reporting System (FARS) data from 1986 to early 1996. FARS is a census of fatal crashes in the United States. Two statistical methods are used to assess fatality reduction. The first hinges on the fact that millions of cars and light trucks have an air bag for the driver, but not the right-front passenger; the ratio of driver to passenger fatalities in these vehicles is compared to corresponding ratios in similar vehicles with air bags at neither position, or at both. The second method hinges on the fact that air bags are primarily designed to deploy and have potential benefits in frontal crashes; the ratio of frontal to nonfrontal fatalities in vehicles equipped with air bags is compared to the corresponding ratio in similar vehicles without air bags. Results by the two methods are averaged. Fatality reductions are described as "statistically significant" if one or (in most cases) both methods show a significant reduction. The report describes how statistical significance is tested and how confidence bounds are calculated.

The primary objective is to find the overall, average fatality reduction by air bags for the entire population of occupants, including those who use their safety belts and those who do not. However, to the extent that the data allow, it is also important to estimate separately the effect of an air bag for an unbelted occupant, and the supplemental fatality reduction by air bags for an occupant who wears safety belts.

The principal conclusion of the study is that driver air bags save lives. The fatality reduction benefit of air bags for all drivers is an estimated 11 percent; this percentage is essentially unchanged from the 1992 and 1994 analyses. New, positive findings are that driver air bags save lives in light trucks and in small cars, that passenger air bags save lives of right-front passengers age 13 or older, and that driver air bags provide a significant supplemental life-saving benefit for the driver who buckles up (as well as saving lives of unbelted drivers).

On the other hand, in-depth crash investigations have revealed 22 cases, as of July 1996, where children may have sustained fatal lesions from interactions with passenger air bags. The accident data now in the FARS are insufficient to determine a specific numerical value for the effect of air bags for child passengers. However, to the extent that preliminary analyses show a higher fatality risk for child passengers age 0-12 in cars with dual air bags than in cars without a passenger air bag, the current data sustain the concerns raised by the in-depth investigations. Statistical analyses also suggest two other possible problems with current air bags: they may have diminished, or even negligible benefits for drivers age 70 or older, and they do not have a statistically significant effect for drivers of any age group in oblique-frontal crashes.

The main findings and conclusions of the evaluation are the following:

AIR BAGS SAVE LIVES

• If no passenger cars or light trucks had been equipped with driver or passenger air bags, it is estimated that a total of 1136 additional fatalities would have occurred during 1986-95 (approximate confidence bounds: 692 to 1622).

OVERALL FATALITY REDUCTION - DRIVER AIR BAGS - PASSENGER CARS

• Air bags reduce the overall fatality risk of car drivers by a statistically significant 11 percent (confidence bounds: 7 to 15 percent). In other words, a fleet of cars equipped with air bags will have 11 percent fewer driver fatalities, total, than the same cars would have had if they did not have air bags.

• Driver air bag effectiveness is holding steady. The estimate of fatality reduction is essentially unchanged from the 1992 and 1994 analyses by NHTSA staff.

PURE FRONTALS VS. PARTIAL FRONTALS - DRIVER AIR BAGS - PASSENGER CARS

• Driver air bags for passenger cars are effective in purely frontal impacts (12:00 damage and no subsequent rollover). The estimated fatality reduction is a statistically significant 30½ percent (confidence bounds: 24 to 37 percent).

• Air bags are significantly less effective for car drivers in partially frontal impacts (11, 1, 10 or 2:00 damage; or 12:00 damage with subsequent rollover) than in purely frontal impacts.

FATALITY REDUCTION - DRIVER AIR BAGS - LIGHT TRUCKS AND VANS

• Driver air bags in light trucks - pickup trucks, vans and sport utility vehicles - are effective in purely frontal crashes. The fatality reduction is a statistically significant 27 percent (confidence bounds: 14 to 40 percent).

• Air bags reduce the overall fatality risk of light truck drivers by a statistically significant 10 percent.

• The preliminary conclusion is that driver air bags are about as effective in light trucks and vans as they are in cars. However, many of the vehicles that first got air bags were minivans. The conclusion will need to be reassessed as more data become available, especially for pickup trucks and sport utility vehicles.

FATALITY REDUCTION - PASSENGER AIR BAGS - CAR PASSENGERS AGE 13 OR OLDER

• Passenger air bags in cars are effective for right-front occupants age 13 or older in purely frontal crashes. The fatality reduction is statistically significant 27 percent (confidence bounds: 9 to 45 percent).

• Air bags reduce the overall fatality risk of car passengers age 13 or older by a statistically significant 13½ percent.

• The preliminary conclusion is that air bags are about as effective for passengers age 13 or older as for drivers. If so, it is estimated that an additional 88 right front passengers age 13 or older would have died during 1986-95 if no passenger cars or light trucks had been equipped with passenger air bags.

PASSENGER AIR BAGS AND CHILDREN AGE 0-12

• The agency's Special Crash Investigation teams, as of July 1996, have identified 22 fatalities of child passengers in low-severity frontal crashes of vehicles equipped with dual air bags (14 before the end of 1995 and 8 during January-July 1996). Infants in rear-facing safety seats, and unrestrained or improperly restrained children who were out of position prior to the main impact, appear to have contacted the air bag during the forceful early phase of its deployment.

• Preliminary analyses of the limited available accident data show increases in fatality risk with passenger air bags for right-front passengers age 0-12 in frontal crashes. The observed effects vary widely, depending on the analysis method, and they are only statistically significant in some of the analyses. In other words, although a specific numerical value on the effect of air bags cannot yet be determined, the results are consistent with the conclusion, from special crash investigations, that child passengers are experiencing problems with air bags.

• The Department of Transportation has formed a coalition with manufacturers, insurance companies and other organizations to prevent injuries and fatalities which may be inadvertently caused by air bags, especially to children. The May 21, 1996 press release announcing the coalition offers the following safety guidelines for child passengers:

  "Infants in rear-facing child safety seats should never be placed in the front seat if the vehicle has a passenger-side air bag. The safest place for children of all ages is the back seat. If riding in the back seat is not an option, toddlers and older children may ride in the front seat of a vehicle with a passenger-side air bag, but only if buckled up properly and with the seat moved as far back as possible."

• On August 1, 1996, NHTSA proposed changes to the air bag requirement with a goal of reducing the risks of air bags to children:

  • The motor vehicle industry is encouraged to begin installing, at the earliest possible date, a 'smart' passenger air bag system that will detect when a child is present and automatically deactivate the air bag or enable it to deploy safely.

  • One kind of 'smart' system that appears to be available now is a weight sensor in the seat that prevents the air bag from deploying when a child is in the seat.

  • Manufacturers who do not provide a qualifying 'smart' system would be required to have new and more prominent air bag warning labels inside the vehicle. They would also be permitted to install cutoff switches so parents can deactivate the passenger-side air bag when a child is seated in front of it.

  • The press release announcing these proposals emphasized that parents can generally eliminate the air bag risk immediately by insisting that their children ride buckled up in the rear seat.

• During 1986-95, as stated above, 14 child passengers apparently received fatal injuries from interactions with passenger air bags in low-severity frontal crashes. During that time, it is estimated that passenger air bags saved the lives of 88 passengers age 13 or older.

OLDER DRIVERS AND AIR BAGS

• The data lead to a preliminary conclusion that air bags are less effective for the driver age 70 or older than for the young or middle-aged driver.

AIR BAG EFFECTIVENESS FOR UNBELTED VS. BELTED CAR DRIVERS

• For drivers reported as unbelted in FARS, air bags reduced fatality risk by a statistically significant 34 percent in purely frontal impacts (confidence bounds: 25 to 42 percent).

• For drivers reported as belted in FARS, air bags reduced fatality risk by a statistically significant 21 percent in purely frontal impacts (confidence bounds: 9 to 33 percent). In other words, in a purely frontal impact, a belted driver has 21 percent lower fatality risk in a car equipped with an air bag than in a similar car without an air bag.

• In States with low belt use, the overall fatality reduction for driver air bags was statistically significant in purely frontal crashes. In States with high belt use, the reduction was also significant, but not quite as large as in the States with low belt use.

• Based on the preceding analyses, it is concluded that air bags save lives for unbelted drivers, and that they save lives for belted drivers.

• It is also concluded that air bags are probably somewhat more effective, in relative terms, for the unbelted driver than for the belted driver.

• The overall fatality reduction by air bags for unbelted drivers in all crashes (not just purely frontal impacts) is estimated to be 13 percent (confidence bounds: 6 to 19 percent).

• The supplemental fatality reduction by air bags for belted drivers in all crashes is estimated to be 9 percent (confidence bounds: 3 to 15 percent).

SMALL VS. LARGE CARS

• The observed overall fatality reduction by air bags is about the same in light-weight, medium-weight and heavy cars. It is concluded that air bags are effective in small cars, and quite possibly no less effective, in relative terms, than in large cars.