Changes in the equilibrium of the urban transport system of a large city following an urban flood

Urban floods are among the most frequent and destructive natural disasters. They generate enormous economic and non-economic losses, including damage to buildings and transportation infrastructure, which are critical systems supporting community well-being. The purpose of this paper was to assess the impact an urban flood would have on the urban road transport system in Łódź and to determine changes in potential accessibility that would accompany a flood. This paper introduces a novel approach in terms of combining the modelling of direct impact ranges of urban flooding in the area of Łódź and a macroscopic multi-motivational traffic model for the city (using PTV Visum software). This made it possible to identify mechanisms of changes made in as many intra-system relationships as possible, as well as between the system and its surroundings. The results showed that changes in the spatial distribution of traffic volume in the city are closely dependent on the water level. The sections of the network most affected by the load changes are those that form the framework for the entire system of Łódź, indicating a lack of resilience of the car transport subsystem in the critical segment for the functioning quality of the entire subsystem. Additionally, the study was conducted for public transport, and it was indicated that changes in its utilization are minimal. It was also found that the greatest impact on transport accessibility from an urban flood is for ultra-short trips. This is primarily due to the base effect (the initial quality of the infrastructure and its potential) – the internal potential of the transport area deteriorates drastically during a flood, severely affecting accessibility.