Occupant injury in longitudinal barrier collisions: effects of restraints.

Longitudinal barriers, such as guardrails, are designed to prevent a vehicle that leaves the roadway from impacting a more dangerous object while minimizing risk of injury to the vehicle occupants. Current full-scale test procedures for these devices do not consider the effect of occupant restraints such as seat belts and airbags. The purpose of this study was to determine the extent to which restraints are used or deployed in longitudinal barrier collisions and their subsequent effect on occupant injury in these collisions. Analyzing national crash data from 1996 through 2005, airbag deployment in longitudinal barrier crashes was found to be 40 percent for all involved vehicles and 68 percent when considering only airbag-equipped vehicles. Seat belt usage rates were approximately 60 and 80 percent for non-airbag-equipped and airbag-equipped vehicles, respectively. Compared to fully restrained occupants, relative risk of injury for no airbag/belted, airbag/unbelted, and no airbag/unbelted occupants was 1.6, 7, and 11.7, respectively. Despite these large differences in relative risk, however, 95 percent of the occupants in the analyzed data were either uninjured or sustained minor injury, which reinforces the overall effectiveness of these roadside devices.