In a disaster situation, road networks play a critical role in maintaining routes for evacuation and logistics. In the event of a catastrophic disaster such as an earthquake, part of the road network may be easily broken into isolated components. In this situation, it is critical that individuals in each district have access to vital facilities in their local neighborhood so that no district is isolated. In this paper, we propose using a topological index (TI) to quantify road network dispersiveness/concentration. Dispersiveness/concentration evaluated by the TI is a valuable approach to evaluate the isolation of districts in a city. We used the index to evaluate dispersiveness/ concentration of a road network in the Hanshin region in Japan, which experienced severe damage in the 1995 Hanshin-Awaji Earthquake. In order to construct the graph for calculating TI, we also present the methodology for specifying effective road links for avoiding functional isolation of districts.
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