Birendra Shrestha

A New Approach for Co-Operative Bus Priority at Traffic Signals

Bus priority at traffic signals is a growing area of cooperative transport system applications. Interest in bus priority continues to grow as the cities pay more attention to the needs of buses to provide fast, frequent, and reliable services, thus contributing to a sustainable transport system. Bus priority at traffic signals is particularly favored at places where road space is limited and traffic signal density is high. With increasing the use of automatic vehicle location (AVL) systems, it is now possible to provide “differential” priority, where different levels of priority can be awarded to buses at traffic signals according to chosen criteria (e.g., to improve regularity). At present, common strategies are based on the comparison of the time headway of a bus with the scheduled headway. However, this paper shows that greater regularity benefits could be achieved through a strategy where priority for a bus is based not only on its own headway but also the headway of the bus behind (the following bus). This paper demonstrates the benefits of this on a theoretical basis and quantifies the benefits from simulation modeling of a high-frequency bus route. Such a strategy provides an opportunity to exploit the more detailed location information available from the growing number of AVL-based systems for buses being implemented around the world.

Investigating bus priority parameters for isolated vehicle actuated junctions

ABSTRACT Bus priority at traffic signals has been implemented in many cities around the world. At signalised junctions, priority can be given by altering signal timings in favour of approaching buses. In usual practice, this is achieved by either extending the green period for an approaching bus or recalling the green stage, if the signal is currently red for the bus. These bus priority methods reduce junction delays for buses and thus improve bus speed and reliability. At isolated junctions in the UK, the parameters used to implement these priority methods are only based on the requirements for green extensions. These parameters may not always be effective for recalls. This study was undertaken to explore whether bus priority benefits can be improved by considering new priority parameters effective for both methods. This research has involved the application of the VISSIM microscopic simulation software to evaluate existing and new strategies for bus priority at isolated signal controlled junctions operating under D-system vehicle actuation (VA). During evaluation, bus travel time savings and impacts on general traffic have been considered. The performance of these methods on various junction types has been evaluated. New advanced bus priority methods based on new priority parameters have been developed and their performance has been compared with the existing methods.

Modelling incidents for dynamic bus fleet management purposes: a UK perspective

Bus operations throughout the world are increasingly being equipped with Intelligent Transport Systems such as Automatic Vehicle Location (AVL). AVL can support a variety of functions, including Dynamic Bus Fleet Management (DBFM), which has yet to be established in most bus fleets in the UK in a systematic way. To develop a fundamental understanding of the bus and traffic related incidents in bus-based public transport for DBFM purposes, a microscopic simulation model, capable of modelling these incidents, has been developed and applied to a variety of scenarios. This paper describes the design and development of the model Simulating Incidents for BUs FlEet Management (SIBUFEM), for modelling bus operations during full-day periods in which incidents of different types can occur. The paper describes the models functionality, including the use of journey time profiles, passenger-dependent bus stop dwell times and deterministic time-dependent queuing theory. Results focus on key performance measures including, but not limited to, bus journey times, passenger waiting times and bus delays resulting from various bus and traffic incidents. SIBUFEM has been applied to a main bus corridor in Southampton, UK, with bus flows increased to produce a high-frequency service. A base case of ‘normal’ operations has been established, for comparison with results from a number of incident scenarios, using key model performance parameters of average bus journey time, bus speed and excess waiting time. Incidents range from bus breakdowns, to traffic incidents such as road-works, traffic accidents and illegal parking. In SIBUFEM, these are specified in terms of their location, duration and severity (loss of capacity). The paper concludes with a discussion on potential DBFM strategies and how the SIBUFEM can be further developed to allow these strategies to be evaluated.