The Contribution of Vehicle, Occupant and Other Factors to the Risk of Injury as a Result of Vehicle Rollover
Injuries and deaths as a result of vehicle rollover have been declining in recent years like other crash modes, but it still remains a consistently large contributor of the overall crash fatalities in the United States. Also, more new vehicles are becoming equipped with electronic stability control and are subject to new regulations that call for increased roof strength and countermeasures to prevent ejection during rollover crashes. It will take several years of production before these newer vehicles permeate the fleet and the effectiveness of these technologies can be fully assessed.
While rollover injury risk has been studied extensively, an assessment of rollover injury causation has not been systematically carried out using both aggregate field data and specific case studies. Also, the contributions of vehicle, occupant and other factors to the injury risk can only be done with specific data analysis targeted at these factors.
The aims of the research described in the following pages are 1) to describe how crash investigations can help deduce the role of vehicle, crash and occupant factors in rollover crash injury risk; 2) to determine the most frequent types of injuries, by body region that occur to belted, unejected occupants involved in moderately severe rollover crashes (2 roof inversions or less). These occupants represent a significant percentage of the rollover fatalities despite their belt use and retention in the vehicle; 3) to analyze this data to deduce the causative factors for these injuries, in particular bony cervical spine injuries; and 4) to use the aggregate and case data analysis to determine potential for test procedures, test tools and countermeasures that can help to reduce the incidence of injury.
Aggregate rollover field data was taken from the National Automotive Sampling System – Crashworthiness Data System (NASS-CDS). Head, spine (cervical) and thoracic injuries dominated the injury with specific injury types in each body region indicating areas of further interest to investigate regarding injury causation. Analysis of specific case studies taken from the Crash Injury Research Engineering Network (CIREN) indicated that single event, single vehicle (pure) rollovers were associated with specific cervical spine injuries that were further analysed for vehicle and occupant factors that may shed light on the injury causation.
The NASS-CDS data for vehicle factors and injury was similar to the CIREN case data. For the CIREN data, the vehicle factor, roof strength (strength to weight ratio), was inversely proportional to the amount of vertical intrusion at the injured occupant location while lateral intrusion was strongly correlated to vertical intrusion when there was 2 roof inversions. The level of cervical injury was also correlated to lateral intrusion (the more lateral intrusion, the lower the primary cervical injury) when there were 2 roof inversions. Occupants tended to be borderline obese (average BMI near 30) regardless of gender and more than half of each gender was a far side (trailing side of rollover) occupant. Average age of the male occupants was 44 while females averaged 37 years of age.