|NHTSA Report Number DOT HS 806 108||February 1982|
Charles J. Kahane, Ph.D.
Head restraints were installed in passenger cars largely in response to Federal Motor Vehicle Safety Standard 202. The purpose of a head restraint is to prevent whiplash injury of the neck in rear impact crashes. The objectives of this Agency staff evaluation are to determine how many injuries integral and adjustable head restraints have eliminated in highway accidents, to measure the actual cost of the restraints, to assess cost effectiveness and to describe the operational performance and problems of integral and adjustable restraints. The evaluation is based on statistical National Accident Sampling System and Fatal Accident Reporting System files; cost analyses of actual head restraint assemblies; a review of laboratory and crash tests and in-depth accident investigations; and head restraint sales data. It was found that:
Whiplash is one of the most common and annoying types of injuries in-motor vehicle crashes. It is by far the predominant injury in rear impact crashes. During the 1960's, more than 400,000 persons a year suffered whiplash when their car was struck in the rear. In the most common form of whiplash, crash forces jerk the victim's head rearward, past the top of the seatback, twisting and injuring the neck.
The logical response to this problem is to effectively raise the seatback and prevent excessive rearward motion of the head. During the 1950's and 1960's, motor vehicle manufacturers and safety research institutions, with the advice of the medical community, devised head restraints which serve the purpose of extending the seatback. There are adjustable restraints which are attached to the seatback and can be moved up or down to suit the occupant. There are integral restraints which are of fixed height and usually a homogeneous part of the seatback.
The General Services Administration mandated head restraints for the front outboard seats of Government cars in 1966 and established criteria for testing the performance of restraints. In 1968, the National Highway Traffic Safety Administration established a head restraint requirement for all passenger cars sold in the United States after January 1, 1969. The requirement and its associated test criteria were promulgated as Federal Motor Vehicle Safety Standard 202.
Executive Order 12291 (February 1981) requires agencies to evaluate their existing major regulations, including any rule whose annual effect on the economy is $100 million or more. This study is an evaluation of the head restraints installed in response to Standard 202, based on the actual operating experience of passenger cars. The evaluation objectives are:
The injury reduction due to head restraints was estimated principally by analyzing three years of Texas accident files. The National Crash Severity Study (NCSS) and a published analysis of insurance claim files provided additional information on injury reduction. NCSS also supplied information on the height and positioning of head restraints in crash-involved cars. The National Accident Sampling System (NASS) yielded a national estimate of the number of persons injured in rear impact crashes during 1979. The effect of head restraints on fatalities was studied by analyzing Fatal Accident Reporting System (FARS) files for 1975-80, the Multidisciplinary Accident Investigation file and long-term fatal accident trends. The cost of head restraints was calculated by disassembling and analyzing the individual components of a representative sample of head restraints and seatbacks. Detailed sales data for head restraints in model years 1977-81 were acquired and studied.
The results from the Texas, NCSS, NASS and FARS analyses were compared to published statistical studies of head restraints, including a major study of insurance claims. Laboratory and crash tests were reviewed, as were selected accident and injury case histories. The research, rulemaking and enforcement activities related to Standard 202 were discussed with Agency engineers and the public Docket was studied. The conclusions of this evaluation are based on all of the information sources - statistical, clinical and engineering.
The most important conclusions of this evaluation are: (1) Head restraints - both the integral and adjustable types - have significantly reduced the number of injuries in rear impact crashes. (2) Integral seats are significantly more effective than adjustable restraints. The first conclusion is based on statistically significant findings from Texas and insurance claim files. The second is based on statistically significant results from Texas and NCSS. The statistical findings, moreover are consistent with engineering intuition, clinical analyses and test results.
The principal shortcoming of the evaluation was that the National Crash Severity Study, the National Accident Sampling System and other detailed files did not contain a large enough sample of cars without head restraints (i.e., pre model year 1969) for statistically meaningful effectiveness comparisons of head restraints versus no head restraints. As a result, it was necessary to rely on State data which do not explicitly distinguish whiplash from other injuries and which are suspected of reporting biases, especially for older cars. A major analytic effort was devoted to removing or minimizing the biases, so as to make the effectiveness estimates as accurate as possible. This effort resulted in some statistically complex estimates for which only approximate, rather than exact, confidence bounds were obtained.
The conclusions on why head restraints have been effective are intuitive judgements based on a thorough review of the available data sources. The conclusion on why integral restraints have not claimed a larger share of the market is based on analysis of sales data, not on a direct survey of consumer attitudes. The findings on the relationship between restraint height and injury risk are based on a statistical model which, at this time, is just partly verified by in-depth accident or crash test data.
The principal findings and conclusions of the study are the following:
|Number of Victims||Percent of Victims|
|Nonfatal injury and treatment:|
|Percent of Victims|
|Whiplash plus other injuries||18|
Sales of integral restraints
Height and positioning of restraints
Effectiveness of head restraints
|Injury Reduction (%)||Confidence Bounds|
|Integral restraints||17||9 to 25|
(75% of which are not extended)
|10||4 to 17|
|Average of integral and adjustable
(weighted by crash involvement rates)
|13||7 to 19|
Benefits of head restraints
|Number of Injuries Prevented||Confidence Bounds|
|Fleet of 100% integral restraints||85,000||40,000 to 130,000|
|Fleet of 100% adjustable restraints
(75% of which would not be extended)
|52,000||17,000 to 87,000|
|Fleet with 1979 mix of integral and adjustable restraints||64,000||28,000 to 100,000|
Cost of head restraints
|Car Purchase Price Increase||Lifetime fuel Consumption||Lifetime Total Cost|
|Integral restraints||$ 6.65||$ 5.68||$12.33|
|Injuries Eliminated Per Million Dollars of Cost||Confidence Bounds|
|Integral restraints||690||360 to 1,060|
|Adjustable restraints||130||40 to 220|
|1979 mix of integral and adjustable||200||90 to 130|
Effectiveness as a function of head restraint height
|Height of the Restraints||Injury Reduction Relative to Current Restraint Mix||Confidence Bounds|
|31 inches||9||2 to 23|
|30 inches||8||2 to 18|
|29 inches||7||2 to 11|
|28 inches||4||2 to 6|
*As positioned by the occupant
Effectiveness of head restraints
Integral versus adjustable restraints