The geometry of head restraints is important but not, by itself, a full indicator of restraint effectiveness. Dynamic testing provides more information, especially about the active head restraints some auto manufacturers are providing in newer cars. Because both static (geometric measurement) and dynamic head restraint evaluations are important, work is afoot to refine the evaluation procedures for use internationally.
How RCAR assesses geometry
Since 1995, the Institute has been publishing model-by-model ratings of head restraint geometry, based on a set procedure for taking the geometric measurements. The purpose is to facilitate head restraint comparisons among vehicle models. Now a modification of this procedure has become an international standard available from the Research Council for Automobile Repairs (RCAR), a consortium of research centers associated with insurers in 17 countries.
The RCAR procedure evaluates restraint height by measuring the vertical distance between the top of a 50th percentile male head form mounted on a standard H-point machine and the top of the head restraint. This is different from the method specified in the federal standard, which measures along the torso line from the H-point on the vehicle seat to the point at which the torso line intersects an orthogonal line that's tangent to the top of the head restraint. The standard is scheduled for revision, but no changes in this measurement method are planned.
Dynamic tests become more important
Good geometry is only the first step toward designing an effective head restraint. Other characteristics count, too, and some active restraint designs that move into position on impact cannot be evaluated without dynamic testing. Such designs include Saab's active head restraint and the whiplash injury prevention system in Volvos (see Status Report special issue: neck injuries in rear-end crashes, May 22, 1999).
The problem is that the dynamic test specified in the federal standard for more than 30 years is inadequate. An international working group has been charged with finding new dynamic tests that could lead to a global standard for assessing whiplash injury prevention.
The International Insurance Whiplash Prevention Group includes representatives from four insurer-supported research centers, including the Institute. This group will develop procedures for dynamic tests to evaluate and compare seat/head restraint designs. Members of the group say the procedures most likely will be based on sled tests.
Already the international group has ruled out using Hybrid III dummies because of their rigid spines. Both BioRID and RID2 are being considered. And recognizing that women are at greater risk of whiplash injuries, the group is discussing long-range steps that include modifying 50th percentile male dummies or developing a new dummy to represent average-size females. Final test procedures are planned for late this year.
Head restraint geometry:
RCAR ratings compared with current and proposed federal standards
Most people don't adjust their head restraints, leaving them in the "down" position. In most cases, this means the restraints provide little or no protection from whiplash injuries. But even in the unadjusted position, the head restraints still meet the federal requirements that have been in effect for 30+ years. As shown above, the proposed federal standard will require higher head restraints — in fact, as high as restraints currently must be to earn a good, or at least acceptable, rating under procedures specified by the Research Council for Automobile Repairs (RCAR).