Neck injuries occuring in rear impacts, often referred to as "whiplash" injuries, have become one of the most common types of injury in car accidents and the number is growing steadily in many countries. One effect of this is that more than half of the medical insurance compenstaion to car accident victims in, for instance, the United States or Germany is related to "whiplash" injuries.

The alarming increase in injury incidence has increased research and product development efforts worldwide. In 1997 (US early 1998), SAAB introduced the SAAB Active Head Restraint (SAHR) in the all-new 9-5 vehicle as a first application of crash activated systems to mitigate whiplash injuries. In addition to the active head-restraint, the SAHR system comprises design features in the seat-back to control and distribute those loads on the occupant that are generated in rear impacts or during rebound from the restraint system in frontal impacts.

This paper describes biomechanical and technical aspects of the SAHR system. It also shows results from tests of the system. The results demonstrate the capacity of the system to substantially reduce known "whiplash" risk factors such as head retraction and extension, neck bending moment, and shearing and tensile/compressive forces in the neck, for occupants of different sizes in a variety of crash and occupant configurations. Also the newly proposed Neck Injury Criterion (NIC 50 ), which predicts the severity of the so-called S-bending of the neck, is included in the analysis.