Rear Seat Occupant Protection in Frontal Crashes and Its Feasibility

As part of NHTSA’s Rear Seat Occupant Protection Research Program, the Fatality Analysis Reporting System (FARS) and State Data System (SDS) for Florida, Pennsylvania and Maryland were utilized to estimate relative fatality rates and injury risk ratios between the front and rear seat passengers. In addition, a parametric study of rear-seat restraint parameters was performed to assess chest deflection and head excursion trends for different belt load limits, pretensioner location(s) and stroke, and impact speeds with the Hybrid III (HIII) 50 percentile male and 5 percentile female dummies. Simulation data were validated using 48 km/h frontal impact sled tests with a standard belt system in outboard rear seats of a mid-size passenger car buck. The real world data suggests that the fatality and serious injury risk in frontal crashes is higher for older occupants in rear seats than for those in front seats. In addition, the relative effectiveness (to mitigate serious injury and death) of rear seats with respect to front seats for restrained adult occupants in newer vehicle models is less than it is in older models, presumably due to the advances in restraint technology that have been incorporated into the front seat position. The simulations demonstrated that adult dummy injury measures in the rear seat can be reduced by incorporating restraint technology (load limiting and pretensioning) used in the front seat, even in the absence of an air bag and knee bolster for load sharing. A force-limiting belt with a pretensioner in the rear seat can maintain or reduce head excursion relative to a standard belt, while significantly reducing chest deformation and thoracic injury risk. In fact, 42 sets of restraint parameters were identified that reduced both head excursion and chest deflection of the 50 percentile male relative to the baseline belt.