The effects of vehicle mass, speed and safety belt wearing on the causes of death in road traffic accidents.

The present investigation was based on the files of the Boards of Traffic Accident Investigation of insurance companies with regard to those fatal motor-car accidents in Finland during the period 1972-1979, where the driver or front seat passenger had died. The analysis concerned a total of 1197 fatalities. In collisions where the other vehicle had been clearly heavier (mass distribution smaller than 1/5) head injuries were significantly (p less than 0.001) more often found as the main cause of death (57.3%) than was the case when colliding vehicles had approximately the same weight (mass distribution 2/3-3/2), in which case head injuries were found in 37.8% of the cases to be the main cause of death. When the speed was over 80 kph , the number of head injuries as the main cause of death increased significantly (p less than 0.001) in collisions where the vehicles had approximately the same weight (mass distribution 2/3-3/2) and in single accidents of motor-cars. The wearing of seat belts had an effect on the distribution of causes of death in single accidents of motor-cars and in collisions where the vehicles had approximately the same weight but did not effect the distribution of causes of death in collisions where the other vehicle was clearly heavier. In single accidents of motor-cars where the victims had not used seat belts, there were more head injuries (54.2%) as the main cause of death than in victims who had used seat belts (head injuries in 36.8% as the main cause of death). In collisions where the vehicles had approximately the same weight, cervical spine injuries were more common causes of death in victims who had used seat belts than in those who had not (21.3%/13.7%). The mechanism of fatal cervical spine injuries in victims who had used seat belts was the rapid bending of the neck due to maximal deceleration in 38% of cases.