Simulation of departure flow profile at stop lines for signal approach spillover

Current definitions of saturation flow rate for signalized intersections fail to consider spillover conditions along intersection approaches, which are caused by interactions between different directional flows. This study establishes the relationship between discharge flow rate and microscopic lane-changing behavior. Two categories of lane-changing behaviors, namely, efficiency-driven and objective-driven behaviors, have been proposed to formulate a driver's decision-making process for intersection approaches. In addition, the developed lane-changing logic is implemented in an enhanced cell transmission model (CTM) to explore the interactions among directional flows. The results of a variety of simulation scenarios identify three stages of departure flow within a typical cycle, i.e., arrival stage, saturation flow stage and the stage that is subjected to the inflow of a channelized section. A comparison with the commonly assumed stable saturation flow concludes that the saturation flow concept requires modifications to enable the evaluation and optimization of signalized approaches under spillover conditions to be performed for an entire approach instead of solely for individual lanes or lane groups.