In this context, [14] indicate four major courses of action in the disaster planning context: (a) the identification of network elements prone to disasters, (b) their impact on operations and protection requirements, (c) the establishment of resilient infrastructures and (d) the scheduling and allocation of recovery resources. Cases (a)-(c) are part of the pre-disaster planning phase: risks in the transportation network elements and infrastructures are to be identified and upgrade and
retrofit actions
for improving the survivability of a transportation network are scheduled and planned. Planning in the predisaster phase is mostly preventive; apart from the design of new, failure-resistant infrastructures, investment decisions in the form of reinforcement or retrofit actions allow the structural integrity and survivability of network components to be enhanced [40]. Experience has shown however that prevention tasks may be inadequate; both the characteristics (magnitude, space and time extent) of a catastrophic event and the performance of infrastructures are uncertain. In addition, limitations in resources make an extensive deployment of plans for enhancing resilience infeasible, raising thus the need for a criteria-based prioritization of retrofit activities [40]. In the post-disaster phase, the transportation network may suffer severe damages to its elements (highways, bridges, embankments, tunnels), ranging from degradation to full collapse. These may in turn reduce the network’s performance, limit its connectivity or lead to partial loss of functionality. The “surviving” transportation network will be expected to operate under a completely different operating environment and service needs. An impending disaster may, for example, force the evacuation of population. The network should be able to handle the large volumes of outbound traffic but at the same time reserve some lanes and routes for emergency response and relief activities. In a later stage, the same network is expected to support recovery but also daily activities until its full restoration. In this context, post-disaster planning focuses on related response, recovery and restoration actions, which would support evacuation and emergency logistics services and gradually restore network operations to their normal condition. The post-disaster phase can be distinguished into sub-phases according to the timing, status and role of the network [19]: