Roadway Departure Events Using SHRP 2 NDS Data

Roadway departures encompass a particularly dangerous subset of driving events during which a vehicle either crosses the centerline or edge line or otherwise leaves the lane of travel. Each year, roadway departure crashes account for roughly 50% of all fatal crashes reported to the National Highway Traffic Safety Administration. This study’s goal was to evaluate the factors contributing to roadway departure events. The data set used was naturalistic driving data collected during the Second Strategic Highway Research Program (SHRP 2). The full data set consisted of 28,937 driving events with information spanning 70 variables that characterized each event. For all events provided to the research team, reductionists categorized each as either a safety-critical or baseline event and reviewed their variable levels. Analyses determined that numerous driver behaviors and roadway environment elements influenced the odds and severity of roadway departure events. Overall, 80% of the adverse driver behavior categories were found to significantly increase the odds of roadway departure crashes at intersections. Drivers who were intoxicated, cut turns, took turns too widely, or were speeding were significantly overrepresented in roadway departure events. The prevalence data indicated that distracted driving was a very common behavior regardless of segment type or event outcome. More specifically, among the baseline events, drivers performing secondary tasks associated with distracted driving were very common. Throughout the baseline sample (i.e., no incidents), drivers were more likely to be distracted by tasks such as device usage, passenger interaction, personal hygiene, eating, smoking, etc., than performing no secondary tasks at all. Across all roadway departure events, adverse driver behavior was observed in 82% of incidents on tangent segments and 93% of incidents at intersections. Roadway environment changes, such as in pavement surface condition, were found to influence roadway departure frequency and severity. Analyses suggested that maintaining the skid resistance of roadway surfaces, even during inclement weather, may be essential to reducing the occurrence and severity of roadway departure events. Furthermore, roadway departures were overrepresented in incidents where sunlight, glare, headlamps, precipitation, vehicles, or infrastructure were obstructing the driver’s view. Researchers noted that visibility obstructions were significantly more common at intersections than tangent segments.