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Current transportation safety interests involving the use of restraints in school buses, coupled with litigation claims arising from injuries to unrestrained occupants of school buses involved in rollovers, resulted in a study aimed at: understanding the biomechanical response and injury causing factors associated with unrestrained students involved in an actual school bus roll-over accident; and, comparing the unrestrained response condition to the hypothetical response if the students were lap belt restrained in the same rollover. A numerical occupant simulation computer code was used to input vehicle rollover motion to both belted and unbelted occupants. The unrestrained case theoretically duplicated the injury producing conditions that led to serious head and neck injury in certain students.

This study examines in some detail 23 actual rear-impact cases dealing with front seat collapse and compares the findings with similar results from 23 Canadian cases. In addition, seat tests and car-to-car crash tests are utilized to examine the potential hazards and/or benefits of collapsing versus non-collapsing seat systems. Evaluation of the above 46 cases indicates that an extremely high rate of rearward ejection occurs to restrained front-seat occupants subjected to rear impact. The majority of those ejected experienced serious to fatal injuries, either from contact in the rear or outside of the vehicle, when seated in collapsing seats. These results are contrary to some earlier published data and, as such, recommendations are made which could help improve data collection methods so as to better evaluate the issues associated with rear-impact seat strength.

An experimental design strategy is presented for the purpose of obtaining efficient and statistically reliable data for the evaluation of multi-variable parameter effects on crash-impact and passive occupant protection materials. Two methods in particular, the factorial and the box-Behnken, are presented and applied to a variety of energy-absorbing materials including: Ethafoam, Ensolite, Sorbothane, and expanded bead polystyrene. Results of the study suggest that Sorbothane could be used to effectively reduce injury potential in vehicle areas which are size constrained from using lighter but thicker energy-absorbing padding materials. The factorial method is also used to demonstrate qualitative evaluation of data obtained from the National Highway Transportation Safety Administration Thoracic Side Impact Protection Research Program. The results of this phase of the paper indicate the high level of importance associated with side-impact occupant protection materials.