Vulnerability Analysis for Transportation Networks

Michael Taylor

• Publisher: Elsevier
• Year: 2017
• ISBN:
  9780128110119
• Topic: Technology & Engineering
• Subtopic: Transportation & Navigation
• Index: Technology & Engineering

Vulnerability Analysis for Transportation Networks provides an integrated framework for understanding and addressing how transportation networks across all modes perform when parts of the network fail or are substantially degraded, such as extreme weather events, natural disasters, road crashes, congestion incidents or road repair. The book reviews the range of existing approaches to network vulnerability and identifies the application of each approach, illustrating them with case studies from around the world.

The book covers the dimensions of time (hours, days, weeks, months and years), spatial coverage (national networks, regional areas, metropolitan and urbanized areas) and modes (road, urban public transport and national railway systems). It shows how the provided framework can be used to indicate the most suitable accessibility tools and metrics for a particular application. Vulnerability Analysis for Transportation Networks is for academics and researchers in transportation networks and for practicing professionals involved in the planning and management of transportation networks and services.

• Presents the most current, complete and integrated account of transport network vulnerability analysis
• Includes numerous case studies from around the world
• Compares alternative approaches to vulnerability analysis for multiple modes and the applicability of each
• Shows how academic transport network planning and management research development can be applied to actual practice, with special focus on socio-economic and environmental impacts

Chapter One

Introduction

Abstract

This chapter presents an overview of the concepts, theories, and methods adopted for vulnerability analysis of transportation networks, dealing with the identification of critical locations and infrastructure components in those networks, estimation of the potential impacts of network degradation or failure, and planning and design for remedial actions in the case of failures. It discusses the relationship between reliability and vulnerability in transportation networks, and summarizes the core definitions of network vulnerability. The chapter also summarizes the contents of the subsequent chapters of the book.

Keywords

Critical infrastructure; Definitions of vulnerability; Network reliability; Network vulnerability; Risk, probability, and consequence

In the late evening of Sunday, January 5, 1975, the bulk-ore carrier MV “Lake Illawarra” was sailing up the Derwent River in Tasmania, past the city of Hobart on its way to the Electrolytic Zinc Works located close to Risdon. This journey had been made many times before, and at this stage the ship had to sail under the Tasman Bridge. On that evening, however, something was wrong. The “Lake Illawarra” was more than 120 m off course, so that instead of negotiating the navigation channel through the central span of the bridge it struck a glancing blow against one pier and then crashed broadside on into its neighbor. Both piers were demolished, a third pier severely damaged, and three spans of the bridge fell into the estuary. The falling debris struck the vessel which then sank in 35 m of water. Four cars crossing the bridge plunged into the water. Seven crew members died, along with five motorists. This was tragedy enough, but the implications of what might have happened had the collision taken place during a peak demand period were traumatic.

Next morning the full extent of the disaster started to become apparent. Hobart was cut into two. The nearest river crossing was nearly 30 km upstream on poor quality roads, a detour of perhaps 2 h. While 28% of Hobart's population lived on the eastern side of the Derwent, the central business district (CBD) and 94% of the jobs in the city were on the western side, along with the city's major hospitals and other vital facilities and services. The city was paralyzed in the aftermath. Immediate emergency plans were initiated, with an air force helicopter available for emergency medical cases and army landing barges on standby to move ambulances and other emergency vehicles when required. The small existing passenger ferry system was augmented, using vessels brought expressly from Sydney Harbour. A temporary bailey bridge was constructed 5 km upstream of the Tasman Bridge, and opened to traffic in December 1975. The Tasman Bridge was repaired, although it lost its pleasing symmetry. Thus eventually “normal service” could be resumed. Today the Bowen Bridge stands at the site of the bailey bridge, so Hobart has two, separated river crossings—on either side of the zinc smelter. Lock and Gelling (1976) provided a salutary account of the Tasman Bridge disaster and its immediate aftermath from the perspective of the transportation planner.

Here are the inklings of the study of transportation network vulnerability, the impacts of the failure or loss of critical components of transportation infrastructure. More so is the need for planning and scenario investigation of potential impacts of network failures and the identification of critical locations and infrastructure in a network. This interest, and its importance, has long been recognized, for instance Lee (1946) detailed the substantial works done by the British Government to protect its national railway system during World War II, through the installation of additional section of rail track and loops. Unfortunately that paper only indicated the sites selected and the works implemented at them. It did not reveal how the site selection was undertaken.¹

In the present age, the need for vulnerability analysis has widened considerably. Sadly, the organized violence of warfare still exists, and human error of the type involved in the Tasman Bridge disaster is always hovering, but other issues have also become more prominent. Natural disasters such as earthquakes can devastate transportation infrastructure, and while this is an historical problem the increased reliance of societies, economies, and communities on that infrastructure heightens the potential consequences. Extreme weather and its impacts, such as flooding, wild fires, and landslides also present threats to the infrastructure, and climate change stands to exacerbate these. The incidence of terrorism in the early 21st century provides an additional, malevolent threat, especially to public transport systems—urban transit is an open system with large numbers of people occupying constrained spaces and may thus provide attractive targets for those who wish to create mayhem.

This book attempts to describe the development and application of analytical methods aimed at describing potential vulnerabilities in transportation systems, in diagnosing the potential causes of those vulnerabilities and identifying vulnerabilityprone locations, and suggesting remedies to overcome those problems. It does so by drawing on the substantial body of international research and investigation on the topic.

1.1. Origins of Network Vulnerability Analysis

Network vulnerability emerged as a significant area in transportation planning research over the last 15 years or so. While the main driver was the need to consider the performance and impacts of degraded networks, vulnerability analysis became important for researchers and planners for two reasons: (1) the development of concept and theory regarding vulnerability, and (2) the application of the new theory to large-scale, complex transportation networks, usually road networks or urban public transport networks. The degree of complexity of real world networks requires computation efficiency as well as theoretical development for the implementation of vulnerability analysis. The theoretical developments are therefore grounded in realism, by necessity.

In broad terms, network vulnerability deals with the socioeconomic impacts and transport systems performance of degraded transport networks. Thus network vulnerability is not just an interesting topic for research by transport network modelers, it is also of great importance to modern society. Degraded network performance from system failures, disaster situations, or even traffic congestion can have significant social and economic impacts. Network failures, whether full or partial or whether due to natural or manmade events, are of great significance. These failures can range from disasters such as earthquakes and bridge collapses, whose effects may persist for long periods of time, to incident-based congestion episodes of relatively short duration but still with large social and economic impacts. Transportation agencies need well-defined concepts and validated models and tools to test networks for their robustness and resilience to failure at different locations, as an integral part of network design and incident management planning, and indeed planning for emergencies.

The concept of network vulnerability is still relatively new, and it is important to define what is meant by vulnerability. For instance, there are several possible responses to the reduced performance of a degraded network, or in dealing with the perceived risks of degradation at different locations. In some cases, an appropriate response may be to upgrade key transport infrastructure, for instance, by raising structures above expected maximum flood levels or by adding more capacity. But sometimes this simply makes the network more reliant on those key links and more vulnerable to their failure. An alternative approach is to add links to the network. These links may normally be redundant but provide alternative routes when key network links are broken (e.g., see Lee, 1946). At the urban-network level there may already be many such latent alternative routes, but at the regional or national strategic network level this is less likely to be the case. Extra links would make the transport network more robust, but this may add unnecessary cost to the provision of transport infrastructure. The questions are:

1. Where are these locations of potential network vulnerability?

2. What is the best response?

The starting point for study of network vulnerability is the study of transportation network reliability, which has been the subject of intense international research interest since the Kobe earthquake of 1995.

1.2. Network Reliability and Vulnerability

Transport network reliability is the subject of considerable international research interest in recent years (Bell & Cassir, 2000; Bell & Iida, 2003; FHWA, 2016; Lam, 1999; OECD, 2010; Taylor, 2013). Much of this research has focused on congested urban road networks and the probability that a network will deliver a required standard of performance. The urban studies are important, but they are not the only areas of concern, especially when considering the wider implications of transport systems performance. At the regional and national strategic level, accessibility, regional coverage, and interurban connectivity are the primary considerations. In these sparse networks, “vulnerability” of the network can be more important than “reliability,” because of the potentially severe adverse consequences of network degradation. As noted by the Australian Bureau of Transport and Regional Economics (BTRE, 2002) in its analysis of the effects of flooding on road access,

the vast distances involved means that access to alternative services (such as hospitals and business) often do not exist … disruption costs to households, businesses and communities can therefore be more important in rural and remote communities.

In both urban and rural areas, the concept of v...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Chapter One. Introduction
• Chapter Two. Critical Infrastructure, Services, and Locations
• Chapter Three. Methods for Vulnerability Analysis
• Chapter Four. Serviceability Methods
• Chapter Five. Accessibility Methods
• Chapter Six. Public Transport Networks
• Chapter Seven. Integrated Framework for Vulnerability Analysis and Application
• Chapter Eight. Summary Overview and Conclusions
• Appendix A. Network Topology for Transportation Networks
• Appendix B. Capacity of Railway Systems
• Index