Defending Transportation Networks against Random and Targeted Attacks

Abstract

This paper explores several reliability and vulnerability measures for transportation networks and proposes three models for optimal resource allocation for transportation network design or defense to minimize the disruption caused by both random and targeted attacks. The common day-to-day disturbances with less severe consequences are referred to as random attacks, but targeted attacks include both coordinated terrorist strikes and large-scale natural disasters. For random attacks, the major concern would be the reliability of the total system travel time. A robust discrete network design problem is formulated to take into account random attacks in the planning stage. The transport capacity or the unsatisfied demand would be critical in case of emergency evacuation, and law enforcement forces could be deployed to prevent malicious attacks in the first place or to ensure a smooth evacuation operation. The proposed models feature an intrinsic trilevel game structure of the network users, the attacker, and the defender (planner). By exploring the unique properties of the proposed measures and reformulating the problems, the trilevel structure models are reduced to mixed-integer semi-infinite optimization programs. This paper further applies an active-set algorithm, combined with a cutting-plane scheme to solve the proposed models. Numerical examples indicate that the proposed formulations are valid and that the solution algorithm can solve the problems effectively and efficiently. The models for targeted attacks provide practical implications on identifying critical infrastructures for evacuation.