This report summarizes the investigation of whether intelligent advanced warnings of the end of green signal helps drivers negotiate the dilemma zone (DZ) at signalized intersections and identifies behavioral mechanisms for any warning related benefits. Prior research suggested that warnings of end of green can increase slowing and stopping frequency given the dilemma zone, but drivers may sometimes respond to warnings by speeding up. In two simulator studies, six types of roadway or in-vehicle warnings were compared with a no-warning control condition. Using multi-level modeling, mediation models of the behavioral mechanisms underlying the effects of the warnings were tested.
Studies were conducted using driving simulators comparing six types of roadway or in-vehicle warnings with a no-warning control condition. Using multilevel modeling, the study tested mediation models of the behavioral mechanisms underlying the effects of warnings.
- Study 1 - used a single tall pole, a series of short poles, and an in-vehicle display.
- Study 2 - used lane specific warnings.
Warnings led to more stopping at dilemma zone intersections and milder decelerations when stopping compared with no warning. Drivers’ predominant response to warnings was anticipatory slowing approaching the intersection, not speeding up. The increased stopping with warning was mediated by increased slowing.
- Study found anticipatory slowing given warnings generalized to green-light intersections where no warning was given.
- Study found that the lane-specific warnings (e.g., LED lights embedded in each lane) sometimes led to fewer unsafe emergency stops than did non-lane-specific roadside warnings.
- Overall, end of green warnings led to safer behavior in the dilemma zone and on the early approach to intersections.