Group-based optimisation of signal timings using the TRANSYT traffic model

This paper presents the group-based optimisation of signal timings for area traffic control. Using group-based control variables, the optimisation of signal timngs is formulated as a set of non-linear mathematical programs. A conventinal performance index, which is a weighted combination of estimated delays and stops, is evaluated by the traffic model from the well-known stage-based procedure TRANSYT and is used as the optimand, but it is considered here as a function of group-based control variables, the common cycle time, the start time and duration of the period of right of way for each signal group. These programs are then solved by an integer programming method. The cases of specified and unspecified cycle time are both discussed. Together with a previous hill-climbing technique some optimisation heuristics for the optimisation of signal timings using group-based notation are developed. These heuristics consist of a mixture of network-wide steps, in which control variables for signal settings at all junctions are changed simultaneously, and junction-based steps, in which the variables at each junction are changed in turn as happens in TRANSYT. A trial network from Leicestershire, England is used in examples to demonstrate the application and effectiveness of the optimisation heuristics.