Risk Reduction Strategies against Terrorist Acts in Urban Built Environments: Towards Sustainable and Human-Centred Challenges

Terrorist impacts have been increasing over time in many countries, being one of the most significant threats for the Built Environment (BE), intended as a network of open spaces (streets, squares) and facing buildings, and their users. Such risk is affected by a combination of strategic functions and crowd conditions. This work traces, for the first time, the state-of-the-art consolidated Risk Mitigation and Reduction Strategies (RMRSs). Solid RMRS regulatory frameworks from all over the world are collected. The results show how classification criteria distinguish them by attack targets and typologies, effectiveness over time/space, and physical implementation versus management-based deployment. Nevertheless, these criteria seem to be too fragmented, failing in pursuing RMRSs selection in a holistic outlook. Thus, a new classification adopting the BE composing elements (physical elements, layout, access/surveillance systems, safety/security management) as key-factors is provided. Features, dependencies and coordination among them are discussed in a sustainability-based perspective, by showing how the main challenges for RMRSs’ design concern applicability, redundancy, and users’ emergency support. Safety/security management strategies have the overall highest sustainability level and play a pivotal role with respect to the other BE composing elements, which should be planned in reference to them. In addition, a human-centred approach (individuals’ interactions with BEs and RMRSs) will also be needed. These results will support efforts to include simulation-oriented approaches into RMRSs selection, effectiveness and feasibility analyses.