Performance analysis of coordinated traffic signals during transition

Coordinated traffic signals can improve progression and delay times by switching timing plans as traffic conditions change. As cycle and split changes shift capacity where needed, signals shift offsets to maintain or to reestablish progressive flow. Signal offsets dictate, for each main-street green phase, where that green starts in each cycle with the intention of promoting nonstop green waves. To start it earlier or later at a given signal, the options are to shorten one or more intermediate phases or to lengthen one or more intermediate phases (or the main-street phase itself or both phases). Such phase time changes may create a temporary lack of capacity or impose extra delay time. Controllers from all vendors offer transition options to choose from that are differentiated by the amount of offset correction possible per cycle, whether they use a short or a long cycle, and by the distribution of time added to or subtracted from the set of phases. Common transition methods include dwell, maximum dwell, add, subtract, and shortway - all of which were recently incorporated into the CorSim actuated-controller logic. A transient profile analysis method is introduced and demonstrated with a model of a major arterial in Tucson, Arizona, and an additional hypothetical network model. The resulting transient profiles highlight the performance transition behavior that occurs during traffic signal plan transition and that contrasts with assertions previously reported in the literature.