Comparative risk estimation of bridges under fire, impact, and blast hazards: groundwork for prioritisation criteria in the Italian guidelines

Bridges are vital components of transportation networks, supporting economic, social, and emergency response functions. Their long service lives, however, expose them to multiple hazards, including fire, impact, and blast events. Although these anthropogenic events are low in probability, their consequences can be severe, especially when cascading effects occur. This paper presents a foundational framework for estimating the risk profile of existing road bridges under such scenarios, addressing a recognised gap in current national risk management procedures. Three risk models from the literature are applied to a representative sample of 50 Italian road bridges to evaluate their capacity to capture the complexity of low-probability, high-consequence (LPHC) events. Shared risk components—hazard, exposure, and vulnerability—are analysed to identify critical gaps and areas of convergence. The study also explores the role of subjective judgments, data limitations, and methodological assumptions in shaping risk estimates. A comparative analysis reveals the variability and sensitivity of outcomes across different hazard-specific risk models. The proposed framework supports a harmonised approach to risk estimation aligned with Italy’s 2020 national bridge guidelines. Ultimately, the work aims to enhance decision-making, strengthen infrastructure resilience, and improve the integration of anthropogenic risk assessment in bridge management practices.