Effects of collision warning system under different warning timing on driving speed and distance

The study examined impacts of different releasing time of warning with an intersection collision warning system (ICWS) on driver behavior. Forty five participants drove a simulated vehicle through five driving scenes containing seven different unexpected collision events with different releasing time of warning and no warning (control) group was presented to counter balanced with the collision event types. Comparing with no warning group, speed trends had significant differences under different releasing time of warning conditions in this study. The results also indicated that releasing ICWS warnings could reduce driving speed to a hazard event so that drivers would adjust speed more appropriately to respond to collision situation. Considering the time of application of violent deceleration for different releasing time of warning, 3.0 s to 4.0 s before a collision occurred might be a proper time to provide warning. In terms of distance to conflict point with maximum deceleration, different releasing time of warning showed statistically different, which suggested that drivers would reserve more space to clear impending collision with earlier warning. Additionally, with the time of warning released earlier, the time of the maximum deceleration rate appeared earlier. Better designs of effective warning when driving at critical intersections could be derived from these results.