16-21 Wang Feature.indd

BY XUAN WANG INTRODUCTION For actuated signal control at intersections with multilane approaches, detectors are normally placed in each lane. Two types of traffic detection schemes can be utilized for vehicle detection associated with multiple detectors: single-channel detection and lane-by-lane detection.1 The current single-channel detection method connects detectors in all lanes on an approach into a single detection circuit. Therefore, when any detector on the approach senses a vehicle, the controller’s gap-out timer for that phase will reset. The phase only terminates once the entire approach gaps out. Such a detection scheme may cause unnecessary green extensions for a multilane approach based on the desired headway. Lane-by-lane detection, however, is an emerging detection scheme in which each lane is monitored with a separate detector and gap-out timer. Under this method, the vehicle phase for the approach terminates when all lanes have individually reached the desired gap-out condition. Vehicle actuated programming (VAP) is an add-on module of the VISSIM traffic simulation software created to develop userdefined controller logic within the simulation. To simulate the lane-by-lane detection and evaluate its effectiveness, traffic-actuated signal control logic for the detection scheme is coded in VAP, and the VISSIM simulation simulates traffic performance. For a multilane approach, FLAG variables were used to record the status of each lane, and the conditional statement was used to check these FLAG variables at each simulation second. When all of the lanes are flagged to reach the desired gapout condition, the phase for the approach gaps out. With this signal control logic, the lane-by-lane detection scheme can be represented by the simulation model. The primary objective of this article is to use VAP within the VISSIM traffic simulation software to simulate the two detection schemes and compare their performance. VISSIM model comparisons were performed to evaluate how the two detection schemes would affect the performance of an actuated signalized intersection. Several scenarios using different variables such as volume, maximum allowable headway (MAH) and number of lanes were examined to determine which variables affect the performance of laneby-lane detection.