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Vulnerability study of northern Sweden: Objectives

I mportance and E xposure in R oad N etwork V ulnerability A nalysis: A C ase S tudy f or N orthern Sweden. Erik Jenelius Transport and Location Analysis Dept. of Transport and Economics Royal Institute of Technology, Stockholm. Vulnerability study of northern Sweden: Objectives.

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Vulnerability study of northern Sweden: Objectives

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  1. Importance and Exposure in Road Network Vulnerability Analysis:A Case Study for Northern Sweden Erik JeneliusTransport and Location AnalysisDept. of Transport and EconomicsRoyal Institute of Technology, Stockholm

  2. Vulnerability study of northern Sweden:Objectives • Find good measures of the vulnerability of nodes, regions and whole road networks, and the criticality of links • Calculate the measures for large regional networks in reasonable time • Apply measures to the regional network of northern Sweden

  3. Vulnerability and exposure • Vulnerability is a susceptibility to incidents that can result in considerable reductions in road network operability (Berdica, 2002) • Vulnerability contains likelihood and consequence • The exposure of a region to a certain incident is the consequences of that incident for that region

  4. Criticality and importance • A link is weak if the probability of an incident is high, important if the consequences are great and critical if it is both weak and important (Nicholson and Du, 1994) • Link k important for region r Region rexposed to failure of link k

  5. Assumptions for the measures • Incident: a link k is closed • Travel demand xij is fixed during event • User equilibrium • Measure of reduced operability: increased generalised travel cost

  6. Different perspectives • Aggregation: is averaged over OD pairs (i, j) • Unweighted average: Average cost increase per OD pairMeasure of regional accessibility • Travel demand-weighted average: Average cost increase per tripMeasure of economic efficiency

  7. Unsatisfied demand • Closure of link may divide network into disconnected components: infinite travel cost • Finite measure of consequences:unsatisfied demand = number of trips unable to reach their destinations

  8. Road network of northern Sweden • Six northernmost counties of Sweden • Original size:c. 26,989 nodes and c. 60,752 directed links2.0·106 OD pairs • After simplification:4,470 nodes and 6,362 undirected links1.3·106 OD pairs • Travel demand data:vehicles on an annual daily average

  9. Traffic load Population density

  10. The case study:Methods and measures • No congestion effects: fast, exact shortest path algorithm • Travel time tij is used as generalised travel cost • Link travel time = length / (free flow speed from vd-function) • Travel time matrix T = (tij) is calculated initially and after every removed link • Total time consumption: 9-10 hoursNew implementation: 15-20 minutes

  11. Unweighted link importancefor the whole network:Average time increase per OD pair • E4 European highway

  12. Demand-weighted link importancefor the whole network:Average time increase per trip • City segments of E4:Local and regional traffic

  13. Unsatisfied demand-related link importancefor the whole network:Average fraction of trips cut off • Roads near the coast • Boundary effects • Sensitive measure

  14. Worst-case scenario: most important link closedUnweighted municipality exposure:Average time increase per OD pair • Southern and northern parts the most exposed • A few links of the E4 the mostimportant for manymunicipalities

  15. Worst-case scenario: most important link closedDemand-weighted municipality exposure:Average time increase per trip • Local density important • Northwestern parts the most exposed

  16. Worst-case scenario: most important link closedUnsatisfied demand-relatedmunicipality exposure:Average fraction of trips cut off • Northwestern region highly exposed • Middle region unexposed

  17. Future work • Study the sub-network available for heavy transports • Study reduction of exposure by adding new links • The probability part:- models of threats (extreme weather, major accidents, hostile attacks)- identify weak links • Policy implications

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