Although the ability of seat belts to reduce the risk of injury has been recognised for some years, the limits of the protection available from current belt systems have not been fully documented. This study aims to define those limits and describe the nature of the injuries sustained. Particular attention is given to those body areas where loading from the belt itself can cause injury.

The results presented are based on a retrospective in-depth field study of occupants who were using three point belts. The accident sample consists of about 650 restrained occupants, the majority of whom were involved in frontal impacts.

For the head and face, the steering wheel is the major source of injury for drivers. Current legislation does little to control the frequency and severity of facial bone fracture in particular. For the chest, three main compromising factors are identified:​ intrusion into the passenger compartment;​ additional loading from behind;​ occupant age. The progression of chest injury severity, from bruising, through single and multiple rib fracture to thoracic organ injury can also be illustrated. The pattern of rib fracture is examined and shows that the ribs loaded directly by the belt, and in particular the lower ribs, fracture first. Fracture of the lower ribs can also lead to abdominal organ injury from the diagonal section of the belt. With European belt systems, injuries from the lap section have been largely eliminated, and it is the injuries from the diagonal section which can limit the effectiveness of current belt systems as far as abdominal injuries are concerned.

The results of this accident study are discussed with reference to human tolerance and current test procedures.