Models are presented to estimate delay during extended control periods (multiple cycles) when downstream traffic queues are both changing over time and significant enough to disrupt traffic flow from an upstream intersection. The models consist of an upstream demand estimation algorithm, a downstream queue build-up prediction algorithm, a shockwaves propagation and dissipation tracking algorithm, and a mechanism to explicitly capture and feed traffic conditions of current cycles into subsequent cycle's control design. Basic traffic flow properties, signal control parameters, and link geometry are used as inputs. The models are modular and can be incorporated in any size system for one or multiple cycles. The models were applied to a hypothetical system of closely spaced intersections and tested for different traffic flow, control, and geometric conditions. The results show that the delay induced by downstream traffic operations on an upstream intersection can be significant and that it may change with each cycle and could reach equilibrium once traffic flow, downstream queues, and signal control measures stabilize and start replicating over time. The results show that the green ratio, offsets, and spacing between intersections have significant effects on this delay. The macroscopic delay models are validated using a microscopic traffic simulation model. There is a close association between delay and queue lengths from both models.
Abstract