The Effectiveness of Head Restraints in Light Trucks

Marie C. Walz

Federal Motor Vehicle Safety Standard 202 has required head restraints in front outboard positions for all cars manufactured January 1, 1969 and later, for sale in the United States. The National Highway Traffic Safety Administration extended the standard to include light trucks (pickup trucks, vans, and sport utility vehicles with Gross Vehicle Weight Rating less than 10,000 pounds) as of September 1, 1991.

NHTSA's 1982 evaluation of head restraints in passenger cars estimated a 13 percent overall reduction in injuries to drivers in rear impacts. The current evaluation, based on data from eight states (Florida, Indiana, Maryland, Missouri, North Carolina, Pennsylvania, Texas, and Utah) estimates that head restraints reduced overall injury risk in light trucks in rear impacts by a statistically significant 6 percent.

Head restraints have been required at the driver's and right front passenger's seats on passenger cars manufactured January 1, 1969 and later, for sale in the United States, by Federal Motor Vehicle Safety Standard 202. The National Highway Traffic Safety Administration extended the standard to light trucks (pickup trucks, vans, and sport utility vehicles with Gross Vehicle Weight Rating less than 10,000 pounds) as of September 1, 1991.

The purpose of head restraints is to prevent excessive rearward motion of an occupant's head in rear impacts, with the goal of reducing the occurrence of "whiplash" injuries. This report examines the effectiveness, benefits, and costs of head restraints in light trucks, based on statistical analyses of state crash data from calendar years 1993 through 1998.

NHTSA's National Automotive Sampling System (NASS) Crashworthiness Data System (CDS) was used to identify if vehicles were equipped with head restraints, by make-model and model year. Most vans and sport utility vehicles already had head restraints long before September 1, 1991. There are few, if any, comparable vehicles without head restraints on which to perform an analysis. Therefore, the present analysis was necessarily limited to pickup trucks; specifically, to seven high-sales make-models of pickup trucks that shifted from few or no head restraints in one model year to most or all head restraints in the next year, in 1990, 1991, or 1992. With some uncertainty, the effectiveness results for these seven make-models are also assumed to apply to other light trucks, such as vans and sport utility vehicles.

While NASS CDS is valuable for identifying what makes and models had head restraints, the number of rear-impact crashes is insufficient for statistically significant comparisons of injury rates in rear-impact crashes of selected make-models before and after the installation of head restraints. Only state crash data files can provide enough cases for those comparisons.

The evaluation was based on eight state files of calendar years 1993-98 - Florida, Indiana, Maryland, Missouri, North Carolina, Pennsylvania, Texas, and Utah - that are available for analysis at NHTSA, which indicate a vehicle's damage location (rear vs. other), and report the make-model or allow its identification via the VIN. The percent of front-seat occupants who had any type of injury in rear-impact crashes was compared for pickup trucks two model years before and after the installation of head restraints. This effectiveness estimate was adjusted for possible biases due to differences in vehicle age, and for the fact that a small percentage of the vehicles in the "Before" group had head restraints. The analysis comprised 93,954 cases of occupants involved in police-reported rear-impact crashes; of these, 23,807 were injured.

While head restraints are designed to reduce whiplash injury, this report examines the change in injury rate overall. This was done for several reasons. Whiplash can involve so many potential body regions that, when limiting whiplash to cases with only neck or back injury, many true whiplash victims are excluded. Conversely, injuries other than whiplash can occur in the neck and back regions, with similar coding descriptions. In addition, all eight State files analyzed in this evaluation code injuries according to their severity: A = "incapacitating injury," B = "other visible injury," C = "possible injury." Most of the symptoms associated with whiplash are not visible injuries, and they are usually, but not exclusively, coded AC.@ Only three of the state files, Indiana, Pennsylvania, and Utah, provide additional injury information: the body region of the occupant's most severe injury and the type of injury (laceration, fracture, complaint of pain, etc.). Since the principal analysis of the data must encompass all eight States, it will be based on comparing overall injury rates (A + B + C) before and after the installation of head restraints.

The principal finding of this study is that:

• Head restraints reduced overall injury risk in light trucks in rear-impact crashes by an estimated 6.08 percent. This reduction is statistically significant (confidence bounds: 3.49 to 8.65 percent).
• Analyses also suggested that:
• Head restraints are more effective in pickup trucks with minor, non-towaway damage than in those trucks with towaway damage. Injury risk is reduced by an estimated 7.75 percent (confidence bounds: 2.59 to 12.84) in pickup trucks with minor damage, and by 0.33 percent (confidence bounds: -3.92 to 4.53) in pickup trucks with major (towaway) damage.

• In these data, the effectiveness of head restraints in reducing injury was about the same for:
  • Male and female occupants
  • Older and younger occupants
  • Centered and off-center rear impacts
  • Integral and adjustable head restraints
  • Pickup trucks with extended cabs and trucks with a cab that ends directly behind the front seat

If every light truck on the road (including all pickups, vans, and sport utility vehicles) had head restraints in 1999, a total of 14,882 injuries would have been prevented, relative to a fleet of light trucks with no head restraints (confidence bounds range from 8,341 to 21,694). Since 88.40 percent of light trucks were in fact equipped with head restraints by then, the actual number of injuries prevented in 1999 was 13,156 (confidence bounds range from 7,373 to 19,177).