Head restraints--the neglected countermeasure.

In a rear-end crash, if an occupant's head is unsupported it lags behind as the torso is accelerated forward. This causes the neck to change shape, first taking an s-shape and then bending backward in a 'whiplash' motion. This sudden differential movement of the head and torso can cause 'whiplash' injuries to the neck. This paper reviews methods to minimize the differential head/torso movement and reduce the resulting injuries, focusing on the necessary first step for prevention, which is a head restraint that is behind and close to the back of an occupant's head during the crash. The history of head restraints since the 1950s is reviewed, with particular attention to advanced restraint designs that are proving effective in reducing whiplash injury risk in dynamic tests using a new crash test dummy neck and a new neck injury criterion.