The simulation of variable traffic signal control in the Bangkok network

Due to the rapidly rising car ownership in Bangkok, the capital of Thailand , traffic congestion is increasing rapidly. TRAF-NETSIM was selected for th e detailed analysis of Bangkok conditions. However, most traffic signals in Bangkok are controlled by on-site traffic police operating the controllers in manual mode. Hence the cycle time, length of stages and the sequence of stages are dependent on the minute by minute decisions of the traffic poli ce. One of the constraints of TRAF-NETSIM (and most other microsimulation m odels) is that the cycle time can have only one value for the whole network , and the sequence of stages must be in the same order throughout the simul ation period. Therefore, the varying cycle times operated by the police had to be represented as a common value, and the sequence of stages had to be fixed. It was then necessary for simulation purposes to adjust the green ti mes to maintain the observed capacities. The principles in Webster and Cobb e (Traffic signals, Technical Paper No. 56, Road Research Laboratory, H.M.S .O., London, England, 1966) were applied to achieve this.