Delay Analysis of a Traffic Signal Phase Termination Algorithm Using Computer Simulation

Downstream congestion can create additional delay at signalized intersections due to queue spillback, a problem which may be mitigated by using a phase truncation algorithm. The implementation of this algorithm is achieved through the use of a logic processor embedded in an off-the-shelf traffic controller, programmed to terminate the subject phase when flow drops below a specified threshold. Two parameters control the aggressiveness of this algorithm: a filter value which specifies the time before the algorithm begins searching for an opportunity to terminate the affected phase; and the headway value which designates the maximum allowable vehicle gap time before the algorithm terminates the phase. Simulations were conducted to determine the impact of varying these parameters on intersection delay at a test intersection operating under oversaturated conditions. The early termination of a turning movement that is blocked by downstream congestion is shown to alleviate delay for the competing through movement at the intersection. Though overall intersection delay is not significantly impacted under the test conditions, the truncation algorithm may be a viable solution for situations where substantial delay is experienced for the through movements. In addition, the truncation logic also provides a viable tool for reporting downstream restriction problems to practitioners in near real-time.