Measuring spatial accessibility to critical infrastructure: The Access Road Identification model

Natural hazards such as earthquakes or floods can severely disrupt transportation networks and lead to cascading effects to other critical infrastructure (CI). A functioning road network is crucial to maintain spatial accessibility of CI such as hospitals or fire stations, especially during disaster scenarios. In the present study, we introduce a geographic information system (GIS)-based model that is able to identify and quantify the access roads to CI facilities through shortest path analysis, namely the Access Road Identification (ARI)-model. Including hazard maps into the model allows comparing CI accessibility in a baseline scenario with a hazard scenario. We exemplary apply the elaborated model to two case studies considering the accessibility of hospitals during floods in Hamburg, Germany and fire stations during an earthquake event in the Tehran-Karaj metropolitan region, Iran.

The results show significant differences between the two case studies: Floods have an overall low impact on the accessibility of hospitals in Hamburg, but single hospitals lose up to 40 % of their access roads during the flood. In Tehran-Karaj however the model indicates that about 38 % of the fire stations have access roads exposed to the earthquake hazard, while a fifth of them lose over 50 % of their access roads and four facilities are completely inaccessible.

These findings highlight the need for robust contingency planning by identifying and prioritizing CI facilities that are most at risk. The novelty of the ARI-model consists in its facility-centered approach to measure spatial accessibility of single CI services, thus unveiling valuable insights regarding the potential loss of direct access roads. The transferability of the model allows to adapt it to various use cases, where different hazards or CI facility types are considered. The model can serve relevant stakeholders as a decision-making tool for prioritizing resource allocation, planning evacuation measures and enhancing disaster preparedness based on CI accessibility, thus being applicable both to the preparation and response phase of disaster management. In the future, an extension of the ARI-model is planned by implementing dynamic hazard maps, data on traffic demand and additional weighting of the results.