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Large-Scale Road Network Vulnerability Analysis
KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Transport and Location Analysis.ORCID iD: 0000-0002-4106-3126
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Disruptions in the transport system can have severe impacts for affected individuals, businesses and the society as a whole. In this research, vulnerability is seen as the risk of unplanned system disruptions, with a focus on large, rare events. Vulnerability analysis aims to provide decision support regarding preventive and restorative actions, ideally as an integrated part of the planning process.The thesis specifically develops the methodology for vulnerability analysis of road networks and considers the effects of suddenly increased travel times and cancelled trips following road link closures. The major part consists of model-based studies of different aspects of vulnerability, in particular the dichotomy of system efficiency and user equity, applied to the Swedish road network. We introduce the concepts of link importance as the overall impact of closing a particular link, and regional exposure as the impact for individuals in a particular region of, e.g., a worst-case or an average-case scenario (Paper I). By construction, a link is important if the normal flow across it is high and/or the alternatives to this link are considerably worse, while a traveller is exposed if a link closure along her normal route is likely and/or the best alternative is considerably worse. Using regression analysis we show that these relationships can be generalized to municipalities and counties, so that geographical variations in vulnerability can be explained by variations in network density and travel patterns (Paper II). The relationship between overall impacts and user disparities are also analyzed for single link closures and is found to be negative, i.e., the most important links also have the most equal distribution of impacts among individuals (Paper III).In addition to links' roles for transport efficiency, the thesis considers their importance as rerouting alternatives when other links are disrupted (Paper IV). Such redundancy-important roads, found often to be running in parallel to highways with heavy traffic, may be warranted a higher standard than their typical use would suggest. We also study the vulnerability of the road network under area-covering disruptions, representing for example flooding, heavy snowfall or forest fires (Paper V). In contrast to single link failures, the impacts of this kind of events are largely determined by the population concentration, more precisely the travel demand within, in and out of the disrupted area itself, while the density of the road network is of small influence. Finally, the thesis approaches the issue of how to value the delays that are incurred by network disruptions and, using an activity-based modelling approach, we illustrate that these delay costs may be considerably higher than the ordinary value of time, in particular during the first few days after the event when travel conditions are uncertain (Paper VI).

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , ix, 45 p.
Series
Trita-TEC-PHD, ISSN 1653-4468 ; 10:005
Keyword [en]
vulnerability, risk reliability, transport, infrastructure, road network
National Category
Other Social Sciences not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-24952ISBN: 978-91-85539-63-5 (print)OAI: oai:DiVA.org:kth-24952DiVA: diva2:354583
Public defence
2010-10-19, D3, Lindstedtsvägen 5, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20101004Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2010-10-04Bibliographically approved
List of papers
1. Importance and exposure in road network vulnerability analysis
Open this publication in new window or tab >>Importance and exposure in road network vulnerability analysis
2006 (English)In: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, E-ISSN 1879-2375, Vol. 40, no 7, 537-560 p.Article in journal (Refereed) Published
Abstract [en]

The reliability and vulnerability of critical infrastructures have attracted a lot of attention recently. In order to assess these issues quantitatively, operational measures are needed. Such measures can also be used as guidance to road administrations in their prioritisation of maintenance and repair of roads, as well as for avoiding causing unnecessary disturbances in the planning of roadwork. The concepts of link importance and site exposure are introduced. In this paper, several link importance indices and site exposure indices are derived, based on the increase in generalised travel cost when links are closed. These measures are divided into two groups: one reflecting an "equal opportunities perspective", and the other a "social efficiency perspective". The measures are calculated for the road network of northern Sweden. Results are collected in a GIs for visualisation, and are presented per link and municipality. In view of the recent great interest in complex networks, some topological measures of the road network are also presented.

Keyword
Contingency planning, Road network topology, Travel reliability, Vulnerability index
National Category
Other Social Sciences not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7575 (URN)10.1016/j.tra.2005.11.003 (DOI)000237913200001 ()2-s2.0-33645902544 (Scopus ID)
Note

QC 20100917

Available from: 2007-11-06 Created: 2007-11-06 Last updated: 2016-05-30Bibliographically approved
2. Network structure and travel patterns: explaining the geographical disparities of road network vulnerability
Open this publication in new window or tab >>Network structure and travel patterns: explaining the geographical disparities of road network vulnerability
2009 (English)In: Journal of Transport Geography, ISSN 0966-6923, Vol. 17, no 3, 234-244 p.Article in journal (Refereed) Published
Abstract [en]

Inevitably, links in the road network are sometimes disrupted because of adverse weather, technical failures or major accidents. Link closures may have different economic and societal consequences depending on in which regions they occur (regional importance), and users may be affected differently depending on where they travel (regional exposure). In this paper we investigate in what way these geographical disparities depend on the road network structure and travel patterns. We propose aggregate supply-side (link redundancy, network scale, road density, population density) and demand-side (user travel time, traffic load) indicators and combine them in statistical regression models. Using the Swedish road network as a case study, we find that regional importance is largely determined by the network structure and the average traffic load in the region, whereas regional exposure is largely determined by the network structure and the average user travel time. Our findings show that the long-term vulnerability disparities stem from fundamental properties of the transport system and the population densities. Quantitatively, they show how vulnerability depends on different variables, which is of interest for robust network design.

Keyword
Vulnerability, Reliability, Regional, Geography, Network, Transport, Road
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-24934 (URN)10.1016/j.jtrangeo.2008.06.002 (DOI)000266306600009 ()2-s2.0-64749109812 (Scopus ID)
Note
QC 20101004.QC 20120208Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2012-02-08Bibliographically approved
3. User inequity implications of road network vulnerability
Open this publication in new window or tab >>User inequity implications of road network vulnerability
2010 (English)In: Journal of Transport and Land Use, ISSN 1938-7849, Vol. 2, no 3/4, 57-73 p.Article in journal (Refereed) Published
Abstract [en]

An important purpose of the road transport system is to allow people to commute in efficientand reliable ways. For various undesired reasons, however, link capacities are sometimes reduced or linksare closed completely. To assess and reduce the risk of such events, a key issue is to identify road linksthat are particularly important, i.e. roads where disruptions would have particularly severe consequences. This paper presents a method for incorporating user equity considerations into a road link importancemeasure. As a complement to measuring the total increase in vehicle travel time, we also measure thedisparity in the distribution among individual users. These two components are combined to form anequity-weighted importance measure. We study the properties of this measure both analytically and in afull-scale case study of the Swedish road network. A main result is that increasing the weight put on theequity aspect transfers importance from the main roads to smaller local roads. The use of the measure intransport policy and planning is discussed.

Keyword
Transport, Networks, Efficiency, Equity, Vulnerability, Reliability
National Category
Other Social Sciences not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-24936 (URN)10.5198/jtlu.v2i3.16 (DOI)
Note

QC 20101004

Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2016-05-16Bibliographically approved
4. Redundancy importance: Links as rerouting alternatives during road network disruptions
Open this publication in new window or tab >>Redundancy importance: Links as rerouting alternatives during road network disruptions
2010 (English)In: Procedia Engineering, 2010, Vol. 3, 129-137 p.Conference paper, Published paper (Refereed)
Abstract [en]

We consider the importance of road links as backup alternatives when other links in the network are disrupted (due to events such as floods, landslides, car accidents etc.). While traditional measures of link importance capture a link’s role for transport efficiency under normal conditions, we are interested in a link’s role for transport robustness and network redundancy. We refer to this concept as redundancy importance and introduce two measures based on traffic flow and disruption impacts (here operationalized as travel delay), respectively. In the flow-based measure we consider the net traffic flow that is redirected to the studied link when other links are closed. In the impact-based measure we also consider the impact that is avoided through the studied link, i.e., how much worse the next-best backup alternatives would be if the studied link itself would not be available. We argue that although a link may not be important under normal conditions, a higher prioritization in resource allocations could be justified if many users could come to rely on it in extraordinary situations. Hence, these measures should be useful as quantitative decision support in the allocation of resources for investments and maintenance as well as for setting up pre-emptive rerouting plans. The measures are applied in a case study of northern Sweden and the general characteristics that determine which links are redundancy important are identified.

Keyword
Network, Vulnerability, Redundancy, Importance, Rerouting, Backup
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-24937 (URN)10.1016/j.proeng.2010.07.013 (DOI)000282748400012 ()2-s2.0-78650556729 (Scopus ID)
Conference
1st Conference on Evacuation Modeling and Management
Note

1st Conference on Evacuation Modeling and Management. QC 20120208

Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2017-12-07Bibliographically approved
5. Road network vulnerability analysis of area-covering disruptions: A grid-based approach with case study
Open this publication in new window or tab >>Road network vulnerability analysis of area-covering disruptions: A grid-based approach with case study
2012 (English)In: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, Vol. 46, no 5, 746-760 p.Article in journal (Refereed) Published
Abstract [en]

We present an approach to systematically analysing the vulnerability of road networks under disruptions covering extended areas. Since various kinds of events including floods, heavy snowfall, storms and wildfires can cause such spatially spread degradations, the analysis method is an important complement to the existing studies of single link failures. The methodology involves covering the study area with grids of uniformly shaped and sized cells, where each cell represents the extent of an event disrupting any intersecting links. We apply the approach to the Swedish road network using travel demand and network data from the Swedish national transport modelling system Sampers. The study shows that the impacts of area-covering disruptions are largely determined by the level of internal, outbound and inbound travel demand of the affected area itself. This is unlike single link failures, where the link flow and the redundancy in the surrounding network determine the impacts. As a result, the vulnerability to spatially spread events shows a markedly different geographical distribution. These findings, which should be universal for most road networks of similar scale, are important in the planning process of resource allocation for mitigation and recovery.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Area, Disruption, Road network, Robustness, Transport, Vulnerability
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-24941 (URN)10.1016/j.tra.2012.02.003 (DOI)000303360000002 ()2-s2.0-84859156445 (Scopus ID)
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20120427Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2012-06-11Bibliographically approved
6. The traveler costs of unplanned transport network disruptions: An activity-based modeling approach
Open this publication in new window or tab >>The traveler costs of unplanned transport network disruptions: An activity-based modeling approach
2010 (English)Conference paper, Published paper (Refereed)
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-24945 (URN)
Conference
Fourth International Symposium on Transport Network Reliability (INSTR)
Note

QC 20101004

Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2016-05-16Bibliographically approved

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