Impact assessment on spatial connectivity and simulation of traffic flows under flood-related road network disruptions

Road networks serve as a critical lifeline for ensuring the mobility of people and goods. The increasing frequency and unpredictability of extreme weather events highlight the need for studies to identify potential vulnerabilities of road networks and assess the negative effects of disruptions on traffic flows. This paper investigates the vulnerability of road networks to flood-induced disruptions, emphasising the use of open data and open-source software tools. Two quantitative approaches are proposed and compared: (i) a GIS-based spatial and topological analysis that assesses network vulnerability without incorporating traffic demand, and (ii) mesoscopic traffic simulation with dynamic traffic assignment to evaluate network performance and functionality under disrupted conditions. These methodologies are applied to a case study in Northern Italy, highlighting their different levels of complexity and applicability depending on data availability. The results indicate that while the spatial and topological approach provides a preliminary identification of vulnerabilities, the simulation method offers a detailed understanding of the dynamic traffic flows under degraded conditions, capturing not only changes in travel distance and time but also the effects of congestion.