Driver decision making at traffic signals

The driving task at signalized road intersections is simplified substantially over that at nonsignalized ones. At the guidance level, the decision-making process consists mainly of the stopping/nonstopping decision at the moment that the signal changes from green to yellow. Most red light running offenses appear to be related to this particular moment. The results of a 1-year before-and-after behavioral study in the northern part of the Netherlands demonstrate that a yellow interval of appropriate length (4 s for 50 km/hr and 5 s for 80 km/hr intersections) cuts the number of red light violations in half. Compared with fixed time control, vehicle-actuated signal control leads to a 1-s shift in the probability of stopping with respect to the potential time to the stopline at the onset of yellow, illustrating the role of driver expectancy in decision making. Through a comparison of these results with observed behavior at drawbridges and signalized railway grade crossings without gates, it is concluded that the absence of a separate yellow interval at railway grade crossings and drawbridges is disadvantageous. For all situations, a uniform stop signalization should be implemented. This signalization should consist of a steady red signal preceded by a yellow interval that is properly designed to serve the driver adequately in normal driving as well as to meet minimal driver needs in deteriorated circumstances.