New strategy options for bus priority at traffic signals in London

Hounsell, N.B., Shrestha, B.P., Palmer, S., Bowen, T. and D'Souza, C. (2008) New strategy options for bus priority at traffic signals in London. European Transport Conference 2008, Noordwijkerhout, Netherlands. 06 - 08 Oct 2008.

Abstract

Providing fast, frequent and reliable bus services is considered as the way forward for sustainable transport operations in many cities. As a part of achieving this goal, many cities and bus operators are implementing Automatic Vehicle Location (AVL) system to support comprehensive public transport management, real time passenger information and bus priority at traffic signals. In London, Transport for London (TfL) has recently procured a GPS (Global Positioning System) based AVL system known as iBUS for this purpose. For bus priority at traffic signals, iBUS uses detector locations configured in the on-bus computer (known as “virtual detectors”) to detect buses. In addition to the flexibility in detecting buses, iBUS also has the facility to monitor buses continuously from the control centre to assess their locations. This provides a real opportunity for Tfl to implement more targeted priority to buses. In this context, current research being carried out by the Transportation Research Group (TRG) for TfL is exploring different priority strategies.
Differential priority is a common term used to describe the strategy where different levels of priority are given to buses at traffic signals according to their need. Differential priority can allow a higher level of priority to be given to some buses (e.g. those which are late) and a lower level or no priority to others. The objective of this form of differential priority is generally to produce improved punctuality for low frequency time-tabled services, or improved regularity for higher frequency, headway-based services. Although this type of strategy can help make buses more punctual and reduce passenger waiting time, it gives lower journey time savings compared to the strategy giving priority to all buses. Clearly passengers waiting for a bus gain from improved punctuality, whilst those on board benefit from reduced journey times.
Implementation of a priority strategy depends on the policy objective of the respective authority. Unless the policy is only concentrated on improving passenger waiting time, a strategy giving a more balanced benefit in terms of passenger waiting time as well as the journey time savings could be more appropriate. This could be assessed in terms of economic value of the benefits from a strategy. The outcome of such strategy may be influenced by the route characteristics such as density of bus stops and traffic signals along the route. For example, if there are many signals and very few bus stops, then the balance could be towards journey time savings. Another important issue could be the bus location on its route. For example, punctuality/reliability of an individual route may not be a problem in the location where many services converge (e.g. near city centre). There may also be a possibility of combining strategies of giving priority to all buses or priority to late buses only. Furthermore, a priority strategy taking account also of the headway of the bus behind could be beneficial. This paper will report on the progress and results of research into these options being undertaken by TRG for TfL, and include issues of implementation.

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