A system-based abstraction hierarchy framework for seismic risk assessment of urban transportation networks

Urban transportation networks are critical infrastructure for post-earthquake emergency response, making proactive seismic risk assessment essential. However, existing frameworks often examine transportation components, interdependencies, and cascading effects separately, making it difficult to integrate them into a unified seismic-risk framework for transportation systems. This study introduces the Urban Transportation System Abstraction Hierarchy (UTSAH), a directed graph–based framework integrating abstraction hierarchy theory with network analysis across five hierarchical levels. Within this framework, UTSAH identifies dominant risk drivers and critical transmission chokepoints within a unified hierarchical structure, enabling simultaneous diagnosis of where risk originates and how it propagates. By determining weighted interdependencies among 131 transportation-specific parameters spanning physical, functional, social, governance, economic, and environmental dimensions, UTSAH provides a unified multi-dimensional assessment of seismic risk propagation and cascading effects in urban transportation networks. Based on graph-based analysis, interventions are classified into three strategic objectives: (i) mitigating cascading effects by seismic retrofitting of vulnerable bridges and tunnels and strengthening construction quality control and periodic inspections; (ii) preserving system connectivity by maintaining emergency transportation network continuity and enhancing route redundancy; and (iii) strengthening vulnerable high-level goals by improving accessibility to critical service centers such as hospitals and fire stations. Overall, UTSAH provides a system-oriented decision-support tool for identifying and classifying candidate seismic risk mitigation strategies in urban transportation networks.