Evaluation of Best Practices for Controlling Signal Systems During Oversaturated Conditions (0-5998-S)

This project developed guidelines for effectively combating congestion in traffic signal systems. Simulation experiments revealed that signal capacity is a function of geometry, traffic conditions, and control parameters, and may be significantly less than expected. Researchers found that (1) when blocking occurs, increasing cycle length decreases capacity; (2) lagging phases with heavy demand improves throughput; and (3) a 500-foot single-lane left-turn bay is sufficient when cycle length is set properly. Mitigating traffic congestion in traffic signal systems is not an easy task because common assumptions about capacity are often violated and because demand is difficult to assess when queues have grown beyond certain bounds. Adverse impacts of congestion can often be reduced by proactive management. This strategy requires optimal controller settings, functioning traffic sensors, and properly trained and experienced staff.