Side impact motor vehicle crashes: driver, passenger, vehicle and crash characteristics for fatally and nonfatally-injured rear-seated adults

BACKGROUND Most studies of rear-seated occupants have focused on or included pediatric occupants which may not translate to adults. This study examines passenger, driver, vehicle and crash characteristics for rear-seated adult occupants involved in side crashes. METHODS The National Automotive Sampling System General Estimates System (NASS/GES) for calendar years 2011-2014 was used with accompanying weights to examine the occupant, vehicle and crash characteristics associated with injury in rear-seated adults (n = 395,504) involved in a side crash. A weighted subpopulation analysis includes occupants travelling in a vehicle with an IIHS safety rating (n = 39,208), which was used to control for vehicle safety. Statistical analysis used Chi-square tests and multilevel multivariable logistic regression. Unadjusted and adjusted odds ratios (ORs) are reported with 95 % confidence intervals (95 % CIs). RESULTS Rear-seated occupants on the same side as the crash impact were more likely to be severely/fatally injured than occupants seated on the opposite side (Multivariable adjusted OR: 2.54, 95 % CI: 2.31-2.79), as were those in angle crashes (Multivariable adjusted OR: 10.85, 95 % CI: 9.24-12.73). Rear-seated occupants of belted drivers were 3.28 times more likely to be belted compared to rear-seated occupants of an unbelted driver. In a subpopulation analysis of all same-side crashes, unrestrained occupants were 5.96 times more likely to be severely/fatally injured compared to restrained occupants. CONCLUSION Restraint use was protective for rear-seated adult occupants involved in side crashes, including those in same-side crashes. Angle and same-side crashes are associated with increased injury severity.