Overview
This research project included work in several areas related to the operation of traffic signal systems in oversaturated traffic conditions. Some of the strategies and methods addressed in the guide include metering, gating, turn restrictions, dynamic lane control or assignment, offset weighting, signal control priorities, and negative/backward progression. The researchers developed quantitative measures that characterize the intensity of oversaturated conditions and can be calculated based on high-resolution data from advance detectors and second-by-second phase timing data. This technique measures the length of the overflow queue at the beginning of the red light and estimates the amount of green time that is wasted either by dispersing this overflow queue or by vehicles that cannot proceed due to a downstream blockage. A heuristic procedure was developed to process the measurements of oversaturation and compute green time modifications on an oversaturated route. A methodology assists in the design of timing plans that can improve system throughput and manage queues in oversaturated conditions.
Individual timing plans were designed for three regimes of operation of an oversaturated scenario and the switching time between the plans is also determined by the methodology. It was found that application of these strategies can result in performance improvements over timing plans designed for undersaturated operation by using timing plans that are designed to manage queues on critical routes. An online logic tool was created that can directly use the quantitative oversaturation intensity measures for real-time, traffic-responsive application of pre-configured mitigation strategies. The practitioner guidance assists in the process of matching mitigation strategies with specific oversaturated conditions scenarios using a systems enginnering approach. In general, the project found that there are tangible performance improvements that are achievable in certain types of oversaturated scenarios by applying mitigation strategies that consider overflow queues.
The project produced a two volume document: