NHTSA Report Number DOT HS 808 470August 1996

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

Charles J. Kahane, Ph.D.

Abstract

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

OVERALL FATALITY REDUCTION - DRIVER AIR BAGS - PASSENGER CARS

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

FATALITY REDUCTION - DRIVER AIR BAGS - LIGHT TRUCKS AND VANS

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

PASSENGER AIR BAGS AND CHILDREN AGE 0-12

OLDER DRIVERS AND AIR BAGS

AIR BAG EFFECTIVENESS FOR UNBELTED VS. BELTED CAR DRIVERS

SMALL VS. LARGE CARS

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