The present paper describes effects of lap-shoulder belts for occupants, focusing on rear seated occupants, in relation to collision configuration and seating position. The study was motivated by the need to provide the visual tool to make every passenger wear the seat belt in safety programs. Fatal injury mechanism of rear-seated occupants and kinematics of vehicle are investigated in real world accidents by means of accident reconstruction. The results indicate that most rear seated unbelted occupants received fatal head injury localized as they hit their heads against around center pillar immediately after collision.

Six collision tests simulating the accident cases reconstructed are carried out to elucidate the dynamics and kinematics behavior of rear seated occupants, in which the impact configurations simulating the accident cases, using the same model passenger cars as the accident cases and dummies as passengers. Mainly dynamics and kinematics of dummies are demonstrated with respect to usage and no-usage of lap-shoulder belt and seating position from high speed films and electronic instrumentation. Most unbelted rear-seated occupant has impacted against interior of the vehicle directly. And also an aggressive aspect of rear-seat unbelted occupant to the front-seated occupant was realized on exposing the severe impact through the backrest by the impact.