Traffic Signal Transition in Coordinated Meshed Networks

Transition of signal plans in networks with controlled traffic lights always has a disruptive impact on traffic flow. The extent of these disruptions depends on the transition method, and therefore increases in delay or travel time may be more or less severe. The task of transitioning becomes even more complex in coordinated networks in which new coordination patterns have to be established quickly without inducing major disturbances. Several transition methods exist, some of which are rather abrupt; others are smoother. Many of these methods have been analyzed in simulation studies. Two extensive studies investigated not only transition effects at isolated intersections but also transition effects on coordinated arterials. This paper adds to these studies by investigating transition effects in a meshed network with different coordinated relations. Furthermore, an additional transition method and variations of previously tested methods have been considered. Four scenarios have been set up and simulated. The results of this study are discussed in detail, delivering not only information on the overall performance of each method but also allowing for some further insights into what is happening during transition. Some effects at intersections are induced by transition at that very intersection, while others have to be ascribed to neighboring intersections. Dwell methods are unfavorable for undisturbed transitioning; smooth methods perform better, especially if transition takes no more than three cycles. The results of this study are valuable for both time-of-day signal plan selection and for adaptive traffic control strategies.