As a consequence of growing traffic density in urban areas, time and vehicle actuated traffic controls are more and more often used. This paper presents a research in which flexible traffic light controls were examined for possible safety deficits. It was necessary to prove the following theory: it is suspected in the case of microscopic light control programs with flexible green periods that there is a higher safety risk, in comparison to fixed-time control for drivers who have local road knowledge during the change of signals (from yellow to red). An unexpected red light or a denied green at an "All-Signals-Red-At-Once-Green" -light could lead to unexpected reactions of the road user. Possible conflict situations are emergency braking, rear-end collisions and running the red light. To compare flexible controlled and fixed-time controlled intersections, these types of conflict were analysed. The investigation contained a selection of traffic light controlled intersections in several German cities (e. g. Stuttgart, Würzburg and Aalen). The study encompassed two intersections with fixed-time control, ten intersections with traffic-actuated control and three intersections with "All-Signals-Red-At-Once-Green" control. In a second measuring series at two intersections in Bremen, different control methods were tested under identical local conditions: fixed time control, semi-vehicle-actuated control and fully traffic-actuated control. (Author/publisher)
Abstract