Since 1995 the Insurance Institute for Highway Safety (IIHS) has measured and evaluated the static geometry of head restraints on vehicle seats. Geometry is important because a restraint positioned behind and close to the back of an occupant’s head is a necessary first step toward reducing neck injury risk in rear crashes. In recent years head restraint geometry in new model passenger vehicles has improved steadily. However, a restraint that does not remain close to the head during a crash cannot effectively support the head and neck, so the effectiveness of a restraint with good static geometry may be reduced by poor dynamic response of a seatback or restraint cushion. In addition, the effectiveness of advanced seat and head restraints designed to move during a crash, either to improve geometry or reduce torso accelerations, can be evaluated only in dynamic tests. Thus, good geometry is necessary but, by itself, not sufficient for optimum protection. Dynamic evaluations using a test dummy also are needed to assess protection against neck injury in rear crashes.

Several insurance-sponsored organizations formed the International Insurance Whiplash Prevention Group to develop a seat/head restraint evaluation protocol, including a dynamic test. Tests using this protocol produce substantially different results among seat/head restraint combinations, even among those with active head restraints. IIHS published its first set of evaluations using the protocol in fall 2004. This paper describes the rationale behind the protocol and summarizes the results of IIHS testing so far.