Urban-regional dynamics of street network resilience. The spatial outcomes of Genoa’s and Bologna’s bridge crashes

The configurational approach enables understanding the behaviour of road-network systems in the face of sudden physical disruptions. Previous studies show that Space Syntax analysis can assist in evaluating how urban systems respond to punctual network interruptions, both in the short and medium-term, and help managing associated risks. The events which followed the crash of the Polcevera bridge in Genoa and that of Bologna Borgo Panigale bridge in 2018 demonstrated in practice that localised urban network interruptions can propagate, affecting movement dynamics, well beyond the boundary of a city and compromise the functioning of the regional motorway network. However, representing the associated effects across the urban to the regional network levels remains a challenge due to computational limitations which constrain Space Syntax studies to use simplified networks in their analyses. This in turn causes discrepancies in cross-scale comparisons, as urban and regional road-morphologies are represented at different levels of detail. The paper studies the effects of the two dramatic events from a multi-scale configurational standpoint by comparatively analysing the through-movement patterns of the urban road-, the regional primary- and the regional motorway- circulation systems. The goal of this research is to discuss, using a real-world example as a benchmark for assessment, the viability of adopting the configurational approach to study failure propagation and gauge levels of street network resilience across spatial scales. The results of this study clarify the importance of weak ties for the resilience of road infrastructure systems and further demonstrate the homothetic behaviour of Normalised Betweenness Centrality measures.