Page 33 - Linkline Autumn 2016

Transit Signal Priority (TSP)
Rachel Ivers, Transport Planner
Giving priority to transit vehicles at signalised intersections is one of the most powerful strategies for improving a transit service that operates in separated or mixed traffic. Furthermore, eliminating unplanned stops e.g. at traffic lights is the best way to improve reliability. Advances in technology continue to create new and less-costly means of providing priority, while increased traffic congestion and concerns about air quality, liveability and the cost of rail constructions make the need for transit priority ever more pressing. Early focus of TSP applications was to do with improving speed, reducing operating cost and passenger ride time. Now it has progressed on to mitigating a major source of randomness in operations at intersection delays and improving service reliability. Before TSP, regimes to control the travel time and improve service reliability were through holding early vehicles at control points. However, this only controls early vehicles, it is unable to increase the performance.
At the forefront of the TSP system vehicles are detected through an Automatic Vehicle Location (AVL) system. All buses in the Dublin Bus fleet have an AVL system fitted with a SIRI (service interface for real time information) standard interface for connection to the SCATS (Sydney Coordinated Adaptive Traffic System) which is used by Dublin’s traffic control centre. This allows the traffic control centre to locate buses on the network and make changes to the traffic signals to allow free flow movement of buses through a junction.
SCATS has an intelligent transport system (ITS) port that allows a separate model to be interfaced e.g. for TSP. Therefore a Dublin specific interface module has been designed allowing it to process data and interface with SCATS to provide a feed of public transport data to influence network decisions. This system is called Dublin Public Transport Interface Module for SCATS; otherwise abbreviated to DPTIMS. In order to visualise this geo-spatial data a map based graphical user interface was developed as seen below.
The introduction of TSP to the bus network in Dublin was tested using the NTA’s Greater Dublin Area (GDA) transport model which is a strategic multi-modal, network based transport model covering the Greater Dublin Area (i.e. the counties of Dublin, Meath, Kildare, Wicklow and Louth). The GDA transport model is owned by the
NTA, who are the authority responsible for its maintenance and use. Two bus routes were tested to determine the possible benefits of introducing such as system to the bus fleet and identify any negative outcomes.
Noticeable time savings were recorded on two bus routes along the Clondalkin QBC and Stillorgan QBC when modelled. This has potential benefits including the ability for bus services to increase frequency with the same resourcing, reduce operational cost, reduce travel time for users and increase the level of equality of bus users over the whole bus network and between users of different modes. This is achieved by balancing the travel time between modes who travel from the same origin to the same destination. Minimal negative impacts were noted on the vehicle network.
References
Dublin Bus, 2011. Annual Report & Financial Statements, Dublin: s.n.
Furth, P. G. & Muller, T. H., 2000. Conditional bus priority at signalised intersections: better service quality with less traffic disruption. Transportation Research Record, Volume 1731, pp. 23-30.
O’Brien, B. & O’Donnell, M., n.d. Centralised public transport priority in SCATS. s.l.:Dublin City Council.
van Oort, N., 2011. Service reliability and urban public transport design, s.l.: TRIAL Reseach School.
Figure 1: Map based presentation of the bus positions
The CharTered InsTITuTe of LogIsTICs & TransporT 33
TRANSIT SIGNAL PRIORITY