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So far, analysis of real-world crashes has not made it possible to evaluate the occupant change of velocity in side impact. This change of velocity is the most pertinent of the lateral-collision violence parameters when occupants are exposed to intrusion by car bodies. The present paper describes a method for calculating this parameter, and includes a description of the data that must be collected concerning real-world crashes in order to enable its application. The validity of this method is demonstrated by its application to a series of experimental collisions. The results are highly correlated to the values resulting from the integration of the accelerations found for the pelvis and thorax. The method is then applied to 60 real-world car-to-car side collisions from the accident survey.

In 1344 car-to-car side collisions, the risk of serious or fatal injury to the occupants of struck vehicles seem to increase proportionally to the difference in mass ratios in favor of the striking vehicle. However, in-depth analysis of 63 collisions during which the impact occurred on the side panel of the passenger compartment reveals that the difference in mass ratios is not the principal determinant of injury severity. The frequency and severity of injuries correlates better with the amount of intrusion of the side panel, a type of intrusion which occurs almost systematically, and even at low impact speed, when the bumper and structure in front of the side rail of the striking car override the rocker panel of the struck car.

A large number of experiments involving cadavers - including real-world-accident reconstructions - have been performed for the purpose of enhancing the state of knowledge concerning tolerance levels and protection criteria relevant to side-impact conditions. However, the scatter of the findings, as well as the considerable differences in injury severity levels (differences that cannot be accounted for by age differences alone) have limited the conclusions that it was possible to draw from these investigations in terms of criteria, mainly concerning thoracic protection. The major cause of scatter is the considerable differences in skeleton quality between subjects. Analysis of the rib characterization test findings made it possible to define a thoracic resistance index enabling the establishment of a classification of subjects. This index, which was validated with our sample, allowed us to evaluate the pertinence of the various side-impact protection criteria considered.

One studies the conditions in which occurred side impacts having led to death of 369 car occupants. This sample is representative of the population of fatal collisions having occurred on French roads, in 1980. 28 % of killed were victims of collisions against another private car, 34 % struck a fixed obstacle, 21 % undergone a collision against a truck. The other types of collisions account for 17%. The performances to be reached in order to spare an important number of victims are of a high level. This is measured in function of the distribution of impact violences and occupants' ages.

Since July 1, 1973, the wearing of seat belts by front seat occupants is compulsory in France. This requirement is respected by 60 to 90% of motorists, depending on the type of road. If seat belts were not worn, a 55% increase in fatalities for front seat occupants would be observed. On the other hand, if seat belts were worn by occupants in all seats 100% of the time, fatalities would be reduced by another 30%. Improvements of the seat belt over the past ten years have had a significant influence in the following areas: - Incentives for wearing the belts - Limitation of belt stretch and spool-out - Reduction of the number of submarining cases. In this paper, emphasis is put on the levels of performance which no other sytem has been able to attain, or even equal, and which result in practically guaranteeing protection against the risk of ejection, especially in a side impact or rollover.