Although much progress has been made in the field of passive car safety in the last years, there is still a strong need for safety improvements in rear-end impacts. While rear-end collisions seldom cause fatal injuries, lesions of the cervical spine are known to cause a high societal cost associated with their often long-term consequences.

The critical body region in rear impact cases is the cervical column. The biomechanics are not yet understood sufficiently to define tolerance limits for soft tissue injuries that could be used for the design of restraint systems. Nevertheless, evidence is high that lesions of the cervical column are caused mostly by shear forces during the first phase of the impact. Therefore, the best strategy to reduce the risk of injury is to control the kinematics of the head-neckthorax system during impact in such a way that relative displacements within this system are minimised.

A concept for a car seat offering enhanced safety has been developed and test models have been built. Although this seat has been designed for the Harder conditions in low mass vehicle collisions, the concept can easily be adapted to conventional cars. The seat features an automatically controlled head restraint adjustment mechanism which guarantees a small and relatively well defined distance between the occupant’s head and the head restraint. Based on computer simulations, paddings for the different regions of the seat back and an energy absorbing yielding mechanism of the seat back have been designed in a way that only little relative displacements in the head-neck-thorax system are to be expected even during a severe rear-end impact. Different occupant sizes ranging from the 5th percentile female to the 95th percentile male have been considered.

A series of rear impact sled tests with velocity changes from 12.2 to 38.6 km/h and acceleration levels from 6 to 30 g has been performed using a 50 percentile Hybrid III dummy equipped with the new TRID neck. The measurements show a good correlation with the simulation and the risk of cervical column injuries is considered to be substantially lower than in conventional seats.