Real-world adjustments of driver seat and head restraint in Saab 9-3 vehicles

Whiplash-associated disorder (WAD), commonly denoted whiplash injury, is a worldwide problem. These injuries occur at relatively low changes of velocity (typically <25 km/h) in impacts from all directions. Rear impacts, however, are the most common in the injury statistics. Females have a 1.5-3 times higher risk of whiplash injury than males.  Improved seat design is the prevailing means of increasing the protection of whiplash injury for occupants in rear impacts. Since 1997, more advanced whiplash protection systems have been introduced on the market, the Saab Active Head Restraint (SAHR) being one of the most prominent. The SAHR-which is height adjustable-is mounted to a pressure plate in the seatback by means of a spring-resisted link mechanism.  Nevertheless, studies have shown that seats equipped with reactive head restraints (such as the SAHR) have a very high injury-reducing effect for males (∼60-70%) but very low or no reduction effect for females. One influencing factor could be the position of the head restraint relative to the head, because a number of studies have reported that adjustable head restraints often are incorrectly positioned by drivers.  The aim was to investigate how female and male Saab drivers adjust the seat in the car they drive the most.

The seated positions of drivers in stationary conditions have been investigated in a total of 76 volunteers (34 females, 42 males) who participated in the study. Inclusion criteria incorporated driving a Saab 9-3 on a regularly basis.

The majority of the volunteers (89%) adjusted the head restraint to any of the 3 uppermost positions and as many as 59% in the top position.  The average vertical distance between the top of the head and the top of the head restraint (offset) increase linearly with increasing statures, from an average of -26 mm (head below the head restraint) for small females to an average of 82 mm (head above the head restraint) for large males. On average, the offset was 23 mm for females, which is within a satisfactory range and in accordance with recommendations; the corresponding value for males was 72 mm.  The backset tended to be shorter among female volunteers (on average 27 mm) compared to the male volunteers (on average 44 mm). Moreover, the backset tended to increase with increasing statures.

Incorrect adjustment of the head restraint cannot explain the large differences found between the sexes in the effectiveness of the SAHR system.