Whiplash associated disorders, occurring in car accidents, are an increasing problem worldwide. According to real-life data from police records, the struck car’s velocity change (Δv) and the gender of the occupant are two of the most important factors related to AIS 1 neck injuries.

A new rear-impact ranking of cars based on 4 432 police reported accidents is presented. The ranking concerns the relative neck injury risk and compensates for the influences of car weight and gender. Moreover, some important factors influencing the risk of AIS 1 neck injury are proposed. These include the stiffness, damping and yielding characteristics of the seat-back, the muscle response of the occupant, and the Δv of the struck car and acceleration pulse.

a mathematical model it is shown that the influence from these factors can be explained by a recently proposed neck injury criterion (NIC). This criterion is based on the neck motion at the passage of full neck retraction. In this study the NIC, based on a number of volunteer tests, is analysed and validated. The consequence of injury outcome of an observed overall seat-back stiffening is also discussed.

In conclusion, for Δv below 20 km/h, real-life data show that the geometry of the head restraint is of minor importance. A seat-back with low yielding limit or soft performance may be preferable. Moreover, the new neck injury criterion seems to be a good predictor of real-life neck injuries.