An operational comparison of pre-time, semi-actuated, and fully actuated interconnected traffic control signal systems

Well timed signal systems are capable of decreasing delay, overall travel time and the number of stops along a roadway. However, the mode of operation selected is crucial. With the arrival of actuated signal controllers, many agencies converted from pre-timed controllers to actuated controllers. Actuated controllers are considered smarter than pre-timed controllers since they are able to vary signal timing based upon traffic volumes present. As a result, actuated controllers are the best selection for isolated intersections with variable traffic demand. Pre-timed controllers are not as efficient as actuated controllers but they may be used at isolated intersections with predictable traffic volumes. However, the question remains: What is the best mode of operation for a signal system? To investigate this topic, two suburban arterial signal systems with approximately 1/2 mile signal spacing in southeastern Wisconsin were selected as test systems. High, medium, and low volume periods were determined for each system based on traffic volume counts. Utilizing SIGNAL94 and PASSER II, optimal signal timing was developed for each mode of operation during each volume period. Evaluation of each system consisted of field gathering stopped delay, percent stopped and average running speed. TRAF-NETSIM analyses were completed for each of the test systems operating under semi-actuated and pre-timed modes of operation for each volume period to evaluate the simulation accuracy of TRAF-NETSIM. The output for each simulation includes stopped delay, and percent stopped. Using the data gathered during the evaluation phase, the output from the TRAF-NETSIM analysis was evaluated for accuracy. This research presents recommendations for optimum signal system operation based on traffic volumes. The recommendations suggest a suburban arterial signal system with speeds of 45-50 mph and signal spacing of approximately 1/2 mile operates most efficiently by changing the mode of operation based on volume conditions. In other words, the signal system may operate in the semi-actuated mode of operation for part of the day, the pre-timed mode of operation for part of the day and actuated for the remainder of the day