A decision-support tool for fire risk assessment and mitigation of motorway bridges: A European case study

Fires represent a significant threat to civil infrastructures and structures, including bridges. Bridge fire events are typically triggered by the presence of flammable materials, most commonly involving vehicle accidents or the transport of combustible goods. Despite a lower probability of occurrence than for buildings, the consequences can be high: bridge structural integrity can be severely compromised, potentially leading to substantial economic losses due to repair costs, traffic disruption, and loss of serviceability. In recent years, the frequency and impact of fire incidents affecting transportation infrastructure have increased, highlighting the vulnerability of bridges to such extreme events. However, current bridge design standards and regulations do not provide fire design criteria, resulting in a critical gap in infrastructure resilience assessment. This study aims to develop a risk-based model for assessing fire hazards in highway bridges, intended as a practical decision-support tool for infrastructure managers to identify critical scenarios and prioritise mitigation strategies. The proposed framework integrates key factors, including traffic composition, structural typology, damage scenarios, and their associated direct and indirect consequences. The model is designed to be applicable at the network level, enabling a systematic evaluation of bridge fire vulnerability. The methodology is applied to a real-world case study of a motorway within the Trans-European Transport Corridor, characterised by high volumes of heavy-vehicle traffic and of strategic economic and social importance. Results demonstrate the effectiveness of the proposed approach in capturing fire-risk variability across different bridge configurations and traffic conditions, providing valuable insights for risk-informed decision-making and targeted risk mitigation measures.