Integrating structural and social vulnerability for equitable bridge maintenance prioritisation

As bridge infrastructure ages worldwide, managers face increasingly scarce resources for maintenance and rehabilitation. However, state-of-the-art prioritisation approaches rely on subjective weighting schemes that focus predominantly on structural conditions whilst neglecting social equity considerations. To address these limitations, this study introduces a novel methodology that integrates bridge structural and social vulnerability, incorporates data-driven weighting, includes subsidence susceptibility, and complements the assessment with economic, maintenance, and monitoring evaluations. The method develops a multi-dimensional Bridge Vulnerability Index that enhances traditional metrics with subsidence susceptibility, spaceborne monitoring availability, economic resilience, and inspection burden indicators. Using Principal Component Factor Analysis for objective weighting, these indicators are aggregated across three dimensions: network criticality, damage susceptibility, and adaptive capacity. The relationship between bridge and social vulnerability is then examined through bivariate mapping, creating a county-level socio-structural vulnerability framework for administrative-level resource prioritisation. Applied to 22,298 Californian bridges across 58 counties, the methodology highlighted several Northern California counties as exhibiting the highest compounded vulnerability scores within the framework, where poor bridge conditions coincide with resource constraints and elevated social vulnerability. These findings reveal how traditional approaches prioritising structural health and network importance may inadvertently perpetuate infrastructure-related social disparities by overlooking communities where failures would have the greatest societal impact. Notably, the strong correlation between social vulnerability and good monitoring availability presents immediate opportunities for deploying MT-InSAR technology to support equitable infrastructure management. The framework thus provides transportation agencies with a tool for more equitable resource allocation for enhancing infrastructure resilience while addressing community needs.