ARLINGTON, Va. — In the most comprehensive evaluation of head restraint designs, the Insurance Institute for Highway Safety has found that more than half of all 1997 passenger vehicles measured have poor restraints. Fewer than 3 percent have head restraint designs with good geometry.
The five vehicles with good head restraint geometry are the Honda Civic del Sol, Mercedes E class with restraints that adjust automatically, the Toyota Supra, and two Volvo models — the 850 and 960. In contrast, dozens of vehicles have head restraints that are neither high enough nor close enough to the back of the head to have the potential to protect many people in rear-end collisions.
"A sad showing," says Institute President Brian O'Neill. "This issue hasn't been a priority among automakers. It's a situation that needs to change because to have a good head restraint design, good geometry is the necessary first step."
Head restraints have been required safety features in cars since 1969. Intended to prevent whiplash and other neck injuries in rear-end crashes, these restraints have to be positioned behind and close enough to the backs of people's heads to have the potential to provide protection. However, most head restraints aren't designed for proper positioning.
What makes good head restraint geometry
Two criteria determine good head restraint geometry. The first is height, and a head restraint ideally should be as high as the top of the head. The second criterion is backset, or the distance between the back of an occupant's head and the front of the restraint. This distance should be small — the smaller the better. Backsets of more than about four inches have been associated with increased symptoms of neck injury in motor vehicle crashes. The Institute's head restraint evaluations are based on these two criteria.
How head restraints were evaluated
Each head restraint was first classified into one of four geometric zones according to its height and backset measures. The rating for a fixed restraint is straightforward — the zone into which its height and backset place it also defines its rating. The rating for a head restraint that adjusts in height and/or backset depends on whether it locks in the adjusted position. If it doesn't, its rating is defined by the zone for height and backset in the "down" and/or rear position. If an adjustable restraint does lock, its height and backset are measured in two positions — the "down" one and the most favorable locked position. The final rating is the better of these except that if the adjusted rating is used, it's downgraded a category because so few motorists adjust their restraints. Some car models from BMW and Mercedes have restraints that adjust automatically. These are evaluated in the position to which they adjust for an average-size male, and the ratings aren't downgraded.
Height and backset were measured with the angle of the torso at about 25 degrees, a typical seat back angle. Many vehicles have more than one seat option, and if seat differences affect the head restraint ratings, more than one rating is shown on the list. But if ratings for all seat options in a model are the same, then only one rating is shown. As indicated, some seat options couldn't be found in showrooms to measure.