This document presents a new methodology for assessing the vulnerability of road networks using GIS applications. It describes calculating a vulnerability index based on road design characteristics and identifying critical links. The methodology was applied to a road network in Ogliastra, Italy. Maps showed the most vulnerable central links that are on multiple shortest paths and critical for rescue services. Considering population in the exposure index showed more vulnerable municipalities in more populated areas. The methodology effectively evaluates vulnerability in low traffic, low population density areas and can help prioritize road improvements and emergency management.

1. by F. Maltinti, D. Melis, F. Annunziata
Seventh International Conference on Informatics and Urban and Regional
Planning, University of Cagliari 10-12 May 2012

2. Introduction
Aim
Describing methodology
Case study
Conclusion and Further studies.
input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

3. Transport infrastructures guarantee accessibility
Importance of accessibility during emergency
situations
Knowledge of road network vulnerability is
fundamental to manage risks
input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

4. Studying a new methodology for assessing road
network vulnerability to:
Identify a vulnerability index correlated to
design and geometric characteristics of roads
Identify critical links of a road network to define
improvements priorities
Guarantee accessibility during emergency
situations input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

5. Territorial analysis Road network analysis
Identification of weak
links
Link interruption
Calculation of shortest paths
matrix
Calculation of vulnerability
index
Maps of vulnerability and priority
input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

6. The proposed Total vulnerability index is expressed by:
vulnerktot=vulnerkglob-norm+vulnerkO/Dresc-norm+vulnerkshorth-path-norm
where:
is the normalized indicator for vulnerability assessment
1) vulnerkglob-norm=f[ΣiΣj (tkij-t0ij)] connected to the whole network
[i, j =urban nodes, k=weak links]
is the normalized indicator for the vulnerability
2) vulnerkO/Dresc-norm=f[ΣiΣj (tkij-t0ij)] assessment connected to the rescue operation
[i, =relief operation centres, j= urban nodes destination
of relief]
3) vulnerkshorth-path-norm=f[ΣiΣj (nkij)]
is the normalized indicator for the vulnerability
1 if ∆tkij>0 assessment connected to the number of shortest paths
nkij= involved in a link closure
0 if ∆tkij<0 input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

7. The index to assess municipality exposure is:
exposurei=f[(ΣkΣj(tkij–t0ij)]
To consider population the function can be rewrite as follows:
exposureweii=f[Pi/Ptot,ΣkΣj(tkij–t0ij)]
We used:
• ArcView GIS, to record georeference and process data, and finally to realize the
network vulnerability map;
• ArcGis Network Analyst extension to calculate the matrix of the shortest paths,
and also to construct the matrix of road distances.
We have obtained travel time by dividing the length by the travel speed of the road
link and travel speed by the design characteristics of the horizontal alignment of the
road to which the link belongs
input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

8. Hypotheses (coming from Italian Geometric Design Standards of Roads):
• the vehicle is isolated: its speed is not affected by traffic conditions;
• the road gradient does not influence vehicle speed;
• on tangents the vehicle follows the equations of uniformly accelerated linear
motion until it reaches the designed speed limit;
• on curves vehicle speed depends on the radius of the curves and on the road
category.
The first one is not easily verified, but it appears valid for roads located in sparsely
populated areas with low traffic volume.
input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

9. This road network has been
interrupted because of landslides
and floods on different occasions.
Figure shows the vulnerability map
of the road network.
The methodology was
Central links are the most
applied to Ogliastra road
vulnerable:
network. Ogliastra is a
they belong to different
sparsely populated area
shortest paths
located in Sardinia (Italy).
they are used for rescue
services for which there are no
alternative routes.

10. These figures show municipality exposure to the event:
The figure on the left shows that more vulnerable municipalities are localized in central-
southern area of the region characterized by low population density.
The situation is
completely different
(see the figure on the
right) using function
considering local
population: more
vulnerable
municipalities are
localized in north-
eastern and south-
eastern area of the
region because they are
more populated than
central-southern area
exposurei=f[(ΣkΣj(tkij–t0ij)] exposureweii=f[Pi/Ptot,ΣkΣj(tkij–t0ij)]

11. The proposed methodology:
• expresses vulnerability of a road network considering geometric and design
characteristics of the elements of road.
• attaches more importance to peripheral links which are particularly critical because
they have not alternative paths and their closure can completely isolate an area.
The methodology is specifically effective in areas of low population density and
where traffic flow is poor.
It could represent a new tool for roads administrators to define improvement
priorities and to manage emergency situations.
The study is going on including other road design characteristics (e.g. road gradient),
identifying combinations of link failures and considering different hazards in the
definition of the index.
input 2012, F. Maltinti "Gis applications for vulnerability assessment of a road network"

12. F. Maltinti "Gis applications for vulnerability assessment of a road network"
Seventh International Conference on Informatics and Urban and Regional
Planning, University of Cagliari 10-12 May 2012