N km --A Proposal for a Neck Protection Criterion for Low-Speed Rear-End Impacts

Soft tissue neck injuries sustained in low speed rear-end collisions are of continued concern in road traffic. To assess the risk of sustaining such injuries, various neck injury criteria have been proposed. In this study a new candidate for such an injury predictor called N km was developed. It is based on a linear combination of shear forces acting in the sagittal direction and extension/flexion bending moments, both measured at the occipital condyles. Results from a total of 40 sled tests, all performed using the same test procedure, with various car front seat models, and using a Hybrid III/TRID as well as a BioRID dummy, were evaluated in order to validate the new criterion. Additionally, a mathematical model was set up to determine the behavior of the N km at a higher crash pulse than the one used in the sled tests. It was shown that the new criterion offers the additional possibility to assess the kinematic phase of forward motion. Furthermore, the influence of the seat design on its protective potential could be related to the N km values obtained and thus, the new criterion is eligible to be part of a standard seat test procedure.