Public transport priority schemes: comparing microsimulation with traditional TRANSYT and LINSIG models

Traffic signals are essential traffic management tools in urban conditions. The design of signals has been an evolving science, driven by the need to make best use of available road space, and changing policy objectives, moving away from capacity maximisation or delay minimisation for private vehicles, towards priority operations for public transport, recognising the passenger numbers transported. In addition, many authorities now actively wish to pursue policies aimed at modal shift towards non-motorised and public transport modes, whilst environmental and safety concerns also come into play. Traditional design tools to calculate signal timings in the UK are TRANSYT and LINSIG. These were initially used in two application for congested corridors in Wolverhampton, aimed at designing demand responsive traffic signals that allow for extra priority for public transport. LINSIG and TRANSYT failed to represent the congested corridor properly: * inaccurate representation of blocking back, the vertical queuing assumptions underestimating the interactions between closely spaced junctions * inability to model dynamic changes in demand, particularly pedestrian demand * poor validation, i.e. fit with observed conditions As as alternative design tool a VISSIM microsimulation model was set up to assess the feasibility of public transport prioritisation along the corridor, and to design the appropriate signal timings. This involved manipulation of two aspects of the model: * modelling the operation of a bus lane, and the associated change in behaviour by car drivers * development of a traffic signal optimiser that minimises some measure of delay for road traffic whilst allocating priority to public transport, pedestrians and cyclists. Comparative results show that: * traditional, average flow rate based tools such as TRANSYT and LINSIG have severe limitations in evaluating congested corridors * microsimulation, because of its dynamic and disaggregate nature, can produce a much better fit to observed conditions * the VAP vehicle actuated programming capability of VISSIM enables us to develop a signal optimiser that will both calculate an optimum signal design and show its operation in reality * the additional benefits of microsimulation are the ability to model new system components such as bus lanes, advance stop lines, Puffins and Toucan