Method to evaluate the effect of safety belt use by rear seat passengers on the injury severity of front seat occupants.

Although the effectiveness of seat belts for reducing injury to rear seat passengers in traffic accidents has been well documented, the ratio of rear-seat passengers restrained by seatbelts remains lower than that of drivers or passengers in front seats. If passengers in rear seats do not wear seat belts, they may sustain unexpected injury to themselves when involved in accidents, and also endanger front occupants (drivers or front seat passengers). This paper focuses on the tendency of front seat occupants to sustain severer injuries due to forward movement of passengers in rear seats at the moment of frontal collisions, and evaluates the effectiveness of rear passengers' wearing seat belts in reducing injuries of front seat occupants. Since the occurrence of occupant injuries depends considerably on the crash severity, we proposed to use pseudo-delta V in regression analysis to represent velocity change during a collision when analyzing statistical accident data. As the crash severity can be estimated from pseudo-delta V, it becomes possible to make appropriate estimations even when the crash severity differs in data. The binary model derived from the ordered response model was used to evaluate the influence on the injury level based on pseudo-delta V, belted or unbelted status, gender and age. Occupants in cars with a hood in the case of car-to-car frontal collisions were extracted from the statistical data on accidents in Japan. Among 81,817 cars, where at least one passenger was present, a total of 6847 cars in which all passengers sustained injuries and which had at least one rear seat passenger aboard were analyzed. The number of killed or seriously injured drivers is estimated to decrease by around 25% if rear seat occupants come to wear seat belts. Also, the number of killed or seriously injured passengers in front seats is estimated to decrease by 28% if unbelted rear seat occupants come to wear seat belts. Thus, wearing of seat belts by previously unbelted rear seat passengers is considered effective in reducing not only injuries to the rear seat passengers themselves but also injuries to front seat occupants.