Comparison of injuries in multiple and single event crashes.

Compare injuries for occupants in multiple event (ME) crashes where a less severe event preceded a more severe event to occupants in similar single event (SE) crashes. Occupants in ME crashes from NASS-CDS years 2000-2015 where the most severe event occurred subsequent to a less severe event were matched to occupants in SE crashes where the SE was similar to the most severe event in the ME crash. Occupants were matched based on occupant, vehicle, and crash characteristics and were compared across 21 detailed body regions using conditional logistic regression.Finite element (FE) simulations were performed with human surrogate models (detailed GHBMC and Hybrid III) and in both low- and high-speed conditions (n = 8 total simulations). At each speed, the crash simulations with both human body models reproduced a common multidirectional ME crash scenario, where the second impulse was more severe and similar to the SE impulse. Relative injury risk was assessed, and ME versus SE were computed and compared to those from the field data. 1,663 ME occupants were matched to 3,217 SE occupants. ME occupants had higher MAIS2+ and MAIS3+ injury risk, and showed directionally higher injury risk in all but one body region. Eleven out of the 27 injury groups had higher injury risk in ME (false discovery rate (FDR)<0.1; all p-values < 0.0427). Increased injury risk was seen in some injuries to the head, thorax, lumbar spine, shoulder, and lower extremity (odds ratios >1.54).In FE simulations, ME displayed larger anterior and lateral displacement compared to SE. Head and thorax injury risk was increased in ME simulations by up to 5-fold. The detailed GHBMC and Hybrid III exhibited different kinematics and injury risk across all simulations, as did low- and high-speed conditions. The field data and FE simulations suggest that a first, less severe crash event results in occupants having greater injury risk when they are involved in a second, more severe crash event than if they were involved only in the second event. Several factors could cause this increase in injury risk, such as improper interaction with safety systems and airbags after the first event renders the occupant out-of-position.