The Effect of Head Restraint Geometry

The second major research project undertaken was to examine head restraint geometry (the size and shape of the restraint and its position relative to the occupant's head) and its ability to lock. By measuring the 'geometry' of the head restraint - the distance between the top of the head restraint and the top of an average person's head and the distance between the back of the head and the head restraint front surface - a 'geometric' plot can be calculated. Using one of four 'zones', a head restraint can be then rated as 'Good', 'Acceptable', 'Marginal' or 'Poor'. The rating given depends upon the restraint's size and shape, its adjustment, and whether it locks in the 'up' position. Research has shown that a locking head restraint offers more protection than those that do not lock and that they are more likely to remain adjusted once set.

The work undertaken by Thatcham and other research centres in Canada, US and Australia has resulted in a new international procedure for the static rating of head restraints. Published under the auspices of RCAR, the Research Council for Automobile Repairs, it is the first time a safety rating procedure has been harmonised throughout the world and is influencing vehicle designers to place 'Good' geometry onto their list of safety priorities.

Head Restraint Geometry Ratings have been published for a number of years and now form an integral part of the Thatcham 'Rear Impact Protection' ratings.