Roof Strength and Injury Risk in Rollover Crashes

Vehicle rollover is a major cause of fatality in passenger vehicle crashes. Rollovers are more complicated than planar crashes, and potential injury mechanisms still are being studied and debated. A central factor in these debates is the importance of having a strong vehicle roof. Minimum roof strength is regulated under Federal Motor Vehicle Safety Standard (FMVSS) 216, but no study to date has established a relationship between performance in this or any other test condition and occupant protection in real-world rollover crashes. The present study evaluated the relationship between roof strengths of 11 midsize SUV roof designs and the rate of fatal or incapacitating driver injury in single-vehicle rollover crashes in 12 states. Quasi-static tests were conducted under the conditions specified in FMVSS 216, and the maximum force required to crush the roof to 2, 5, and 10 inches of plate displacement was recorded. Various measures of roof strength were calculated from the test results for evaluation in logistic regression models. In all cases, increased measures of roof strength resulted in significantly reduced rates of fatal or incapacitating driver injury after accounting for vehicle stability, driver age, and state differences. A one-unit increase in peak strength-to-weight ratio (SWR) within 5 inches of plate displacement, the metric currently regulated under the FMVSS 216 standard, was estimated to reduce the risk of fatal or incapacitating injury by 28 percent