Factors affecting injury severity to rear-seated occupants in rural motor vehicle crashes

Injury to rear-seat occupants (RSOs) has received little systematic study in the literature. Past studies have focused on patterns of injury presented to the emergency department, various aspects of restraint usage and injury, or specific populations of RSOs. This is the first systematic analysis of injury severity to RSOs. RSOs involved in motor vehicle crashes (MVCs) sustain injuries of equal severity as do front-seated occupants (FSOs) involved in the same crash. The setting was a rural North Carolina emergency department where patients were evaluated at the sole hospital for the county. The design was a 2-year retrospective review of all MVCs with RSOs occurring in Pitt County North Carolina in calendar years 1988 and 1989. The Wilcoxon Rank-Sum Test and Logistic Regression Analysis with Injury Severity Score (ISS) as the dependent variable were performed. Three hundred forty-six crashes involving 367 vehicles with RSOs and 1,273 occupants that sent 222 patients to the hospital. ISS was higher for unrestrained occupants (1.87 versus 0.51), occupants of vehicles driven by legally intoxicated drivers (4.04 versus 0.73), occupants between the ages of 30 and 59 years (1.06 versus 0.65) and FSOs (1.04 versus 0.85) (Wilcoxon Rank-Sum test P <.0002). Logistic regression analysis confirmed these findings with the exception of more severe injuries for the 30 to 59 age range and impact speed. The analysis failed in these 2 cases. Restraint usage offered the greatest protective effect (OR 0.37). Lesser protective effects were noted with rear seat occupancy (OR 0.43) and age < 13 years (OR 0.77). More severe injuries were predicted by driver intoxication (OR 2.5), and age > 60 years (OR 1.25). In our rural population, RSOs sustain less severe injuries than FSOs. Restraint usage and sober drivers provide a greater protective effect however. Seat location does not replace restraint usage or sobriety.