The purpose of this study is to evaluate the potential for the reduction of occupants neck injuries, so called “whiplash injuries” (whiplash associated disorder), in rear end collisions. Based upon new biomechanical research, an effort was made to design head restraints and seats to help lead to a reduction of such injuries. This resulted in a concept which involves the motion of the head and torso in harmony during a rear end collision. Consequently a newly designed seat based upon this concept is evaluated in low speed rear impact dummy sled tests, and additionally offered in volunteer sled tests using X-ray cinemas conducted by Japan Automobile Research Institute and University of Tsukuba, who investigate the influence of seat characteristics to human head and torso kinematics and cervical vertebra movement to reveal the mechanism of whiplash injuries. As a result, it was found that the motion between head and torso as well as the movement between each cervical vertebra was reduced.