Assessing travel time impacts of measures to enhance bus operations

Road & Transport Research, Dec 1999 by Jepson, D, Ferreira, L

Refereed Paper

This paper has been critically reviewed by at least two recognised experts in the field.

Originally submitted: June 1998

Abstract

There have been a variety of bus priority measures used for at least 25 years throughout the world. European countries, particularly the United Kingdom, have pioneered many of the bus priority systems on arterial streets. Many of the systems associated with freeway operations have been developed in the United States. Bus lanes and traffic signal priority are the most common forms of bus priority, and these systems can provide significant travel time savings for congested arterial roads. This paper presents the main findings regarding evidence from past work and places the topic in the wider transport planning context. The analysis of the various treatments will focus on reducing travel time for buses, which is fundamentally linked to the cost and efficiency of this form of public transport. The work undertaken considers the travel time savings obtained for buses and the associated impacts on the remainder of the general purpose traffic to minimise the person delay through the network. The inclusion of other parameters that may affect the justification of bus priority measures, such as vehicle costs and the environmental costs, is a logical extension of this research.

This paper recommends that bus priority treatments be part of an overall traffic management strategy for a transport corridor. It is suggested that there may be significant travel time savings associated with bus priority treatments. However, to obtain these benefits with manageable impacts on other traffic, the type and nature of the bus priority treatments need to be matched to the road and traffic conditions. This will ensure that the efficiency of the road infrastructure is maximised for each traffic management strategy.

INTRODUCTION

It is recognised that the increasing costs of traffic congestion need to be addressed through an integrated multi-modal transport system. The savings to the community in facilitating a shift to public transport can be significant, particularly in urban peak congested conditions. This may be enhanced through modifications to the service provided by public transport. Improvements to public transport may be considered through a number of avenues including improving vehicle efficiency, integration of transport modes, reduction of the cost of service, reductions in travel times, and improvements in comfort for passengers.

Bus operation efficiency is examined here through single trip journeys for buses on arterial roads to investigate techniques for improving this form of transport. The work reported here was part of a research project, which analysed the travel time savings obtained for buses and the associated impacts on other traffic in order to minimise the person delay through the network.

Whilst optimising person delay is one of the most significant transport goals, it is acknowledged that there are other issues that may influence the decision to implement bus priority treatments. The impact on bus operating costs, the environmental benefits of public transport, and the management of demand for private vehicles are three of the substantial issues that would affect this process. The current analysis was undertaken at a micro level for a specific route and examines only travel time issues. The effects of vehicle operating costs and environmental impacts are not included in this research.

The second section of this paper provides a review of the existing practice for each of the main bus priority measures under study, namely: bus lanes, signal priority, busways, transit lanes and measures related to bus stop delays. The third section considers the assessment of bus priority measures in the context of the wider transport planning objectives. Finally, a summary of the evidence reviewed is presented. This paper represents Part I of a two-part publication in this journal. Part II deals with the development of assessment criteria for each priority measure and the detailed results obtained.

PAST WORK

Background

The main components of the total bus journey time include the road travel time, delay due to acceleration/deceleration at bus stops and the delay associated with the boarding/alighting of passengers. Bus travel time in urban conditions can be typically twice the corresponding travel time for a car. There is a need to understand the components of the total bus journey time to allow this time to be minimised for any route under consideration.

The road travel time for arterial roads is influenced by delays associated with road geometry, traffic control devices (e.g. traffic signals, roundabouts) and interactions with other vehicles. The travel time function has been considered in Australia by Davidson (1978), Akcelik (1991) and Tisato (1991). The prediction of travel time is important in evaluating the effect of changes in traffic conditions. In situations of high vehicle flow there are increased interactions with other traffic and the delays are higher for vehicles using the route. In these circumstances the benefits of bus priority treatments are the most significant.