A Traffic Signal Split Optimization Using Time-space Diagrams
P Lertworawanich, Department of Highways Bangkok, TH
Traffic dynamics at signalized intersections are represented on time-space diagrams. Splits are incrementally adjusted so that the delay per cycle is gradually minimized.
Traffic signals are the main devices for controlling traffic to guarantee the safe crossing of opposing streams of vehicles and pedestrians. As traffic demand increases, signal operations become more important. Efficient signal controls lead to less congestion and smooth operations while poor signal controls could result in severe congestion or even a network gridlock. Dynamic controls, where signal parameters are automatically optimized to the change of traffic demand monitored by detectors, become important. In this study, a simple split optimization method is developed. The proposed methodology is based on the notion of minimizing delay per cycle. Traffic dynamics at signalized intersections are represented on time-space diagrams using the shockwave theory and information from detectors installed upstream of intersections. Splits are incrementally adjusted so that the delay per cycle is gradually minimized. Unlike most algorithms, the proposed method can manage traffic even when queues extend beyond detector locations. Simulation experiments on a single fixed-cycle-length intersection with five demand scenarios are conducted to demonstrate efficiency of the developed algorithm. It is found that in case of fixed demand the proposed method can optimize splits, which eventually converge to the optimal fixed-time signal settings. For the variable demand case, the result indicates that the algorithm can correctly adjust splits in response to the change of demand. The proposed algorithm has demonstrated itself to be a potential split optimization for an adaptive signal control system. In future, this concept of time-space diagram will be expanded to cycle time and offset optimization to complete all components of signal control systems.
Association for European Transport