Real World Analysis of Rear Seat Occupant Safety in Frontal Crashes

The National Highway Traffic Safety Administration’s (NHTSA) Vehicle Safety Rulemaking and Research Priority Plan 2009 – 2011 describes the projects the agency plans to work on in the rulemaking and research areas in those calendar years. Specific programs identified in the plan included research to improve vehicle safety for rear seat occupants, children, and older people. In support of the priority plan, an analysis of realworld crash data was conducted to determine the nature of the crash problem and examine the factors that contribute to rear seat occupant injury, including children and older people. A review of the National Automotive Sampling System Crashworthiness Data System (NASS-CDS) and Crash Injury Research and Engineering Network (CIREN) case data was conducted for restrained rear seat occupants in frontal crashes that sustained an Abbreviated Injury Scale (AIS) 3+ injury in 1998 model year and newer vehicles. For each occupant identified, a review of the accompanying investigation was conducted using a methodology similar to that described by Bean et al. [2009]. The authors were then able to identify occupant and crash characteristics associated with rear seat occupants commonly sustaining serious injuries in frontal crashes. For each occupant, a primary cause of the most severe injury was assigned and injury sources were identified. This review suggests that in the absence of overly severe frontal crash conditions and vulnerabilities due to advanced age, properly belted adults and children in ageand stature-appropriate child restraints are reasonably well-protected in the rear seat, although improvements could be achieved in some cases. INTRODUCTION Fatal crashes decreased by 9.9 percent from 2008 to 2009, and the fatality rate on U.S. roads has dropped to 1.13 per 100 million vehicle miles of travel. The injury rate per 100 million vehicle miles of travel decreased 6.3 percent from the previous year as well [NHTSA, 2010]. While many factors contribute to the reduction in the rate of injurious and fatal crashes, improvements in occupant protection are likely responsible for a sizeable portion of the long-term reduction. Front-row occupant protection in frontal crashes has benefited from recent developments in restraint performance and vehicle crashworthiness, which have been driven partly by manufacturers’ efforts to improve vehicle scores in consumer information tests. Sherwood et al. reported in 2009 that 95% of the 2008 model year cars earned four or five stars in NHTSA’s New Car Assessment Program and 91% earned the highest frontal crashworthiness rating from the Insurance Institute for Highway Safety. While much of the improvement in performance can be likely linked to improved frontal structures, the restraint systems for the occupants tested in those programs have improved as well. Kent et al. [2007] reported steadily increasing availability of seat belt pretensioner and forcelimiting mechanisms, which, at the time, were nearing universal availability in the fleet. Since these advanced restraint technologies have typically been installed only in the first row, where their inclusion helps to improve test scores, occupants in the rear seating area have not seen the same benefits as their front seat counterparts. Many recent studies have focused on the protection offered to rear seat occupants involved in frontal crashes. Some of these studies have found that, for some occupants, rear seating positions are associated with higher injury and fatality risk than front row