Protection of Rear Seat Occupants in Frontal Crashes, Assessment Methodology and Injury Metrics Open Access
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Historically, rear seat positions have been considered safer than front seat positions, especially during frontal crashes. However, recent crash test results, with dummies included in their rear seats, have shown high injury measures for those dummies, exceeding the injury limits proposed by safety standards/ criteria, as well as, the injury readings for front seat occupants. Resolving the controversy between the real world findings and the crash test results motivated this study. To have a proper methodology for estimating effectiveness of the rear seat, possible contributing factors affecting protection of rear seat occupant and possible methodologies to reduce effect of confounding factors were studied. Mathematical development of double paired comparison method was extended, and a new control group selection method was proposed to reduce possibility of bias due to age combination of drivers accompanied by a right front seat occupant versus those accompanied by rear seat occupants. The new method identified biases in prior estimates of effectiveness of rear seats. Application of the new method showed that occupants of all ages were better protected in rear seats when compared to right front seats in older model years of vehicles. However, in new (2000s) model years of vehicles, the restraint occupants of 25+ years old are less protected in rear seats when compared to right front seats. The study continued to identify the causes for the observed trends. It was shown that the increases in front end stiffness of the vehicles due to use of higher strength steel or thicker metal sheets is a significant factor causing the observed trend. To verify the findings, Finite Element (FE) simulations were used. FE simulations further determined the sensitivity of the rear seat occupant protection toother aspects of the structure and crash scenario, and identified body regions that would most suffer from the increase in front end stiffness. The research continued with showing inability of NCAP tests with only front seat dummies for predicting rear seat occupant safety. Addition of a dummy in a rear seating position during standard NCAP tests, and the proper method for interpreting the results were included as the proper criteria to estimate the safety level of the rear seat occupants.