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Rollover accidents account for a large number of serious to fatal injuries annually. In the past, these injuries were often the result of unrestrained occupant ejection. Subsequent to mandatory belt use laws, a larger percentage of these injuries occur inside the vehicle, and the head and neck areas sustain a substantial number of these injuries. An analytical effort to understand rollover injuries, using the field accident data of the NASS files and residual headroom as an indicator, was reported by the authors at the 1996 ESV conference in Melbourne, Australia. This paper describes the relationship between roof crush and restrained occupant injury in rollover accidents as derived from the analysis of 1988-1992 NASS files. It extends the residual headroom parameter to the entire population of head, face and neck occupants injured inside the compartment.1

Rollover accidents account for a large number of serious to fatal injuries annually. In the past, these injuries were often the result of unrestrained occupant ejection. Subsequent to mandatory belt use laws, a larger percentage of these injuries occur inside the vehicle, and the head and neck areas sustain a substantial number of these injuries. Rollovers have been characterized as violent events, roof crush as the natural consequence of such violence. Further, head and neck injury have been thus considered unavoidable, even with occupant use of the production restraints. This paper will describe the relationship between the three dimensional extent (severity) of roof crush and the equivalent drop test contact velocity as derived from physical experiments and tests. The drop test contact velocity is directly related to the cumulative change of velocity experienced by a vehicle as a result of roof contact deformation during a rollover accident by validated computer simulations.

This paper describes some human subject experiments in occupant response to rollover with reduced headroom. The results suggest that with a nominal 10 cm of head room, 7.5 to 15 cm of torso excursion in production belts and more than 15 cm of roof intrusion, serious neck injury is likely. Brain damage/head injury is more likely from a combination of roof rail crush and high change of angular roll rate.

Roof strength clearly affects the probability of occupant head and neck injury in light vehicle rollovers. Despite this, most manufacturers continue to design and build vehicles with inadequate roof strength. From experimental and biomechanics evidence and rollover crash data, we present the case that weak, antiquated roof designs contribute to severe head and neck injuries. We discuss the deficiencies in modern roof designs, how they cause severe head and neck injuries, and the limitations inherent in the Federal roof crush standard, FMVSS 216. We describe cost-effective examples of materials and technologies that can provide adequate roof strength to protect occupants in most rollovers without imposing significant weight penalties. Finally, we discuss an approach to dynamic roof strength testing that is based on what occurs in an actual, serious injury-producing rollover.