In this section, strategic planning issues encountered in multimodal freight transportation and the future development directions are presented. Strategic planning problems relate to investment decisions on the present infrastructures (networks). Table 1 and Fig. 1 provide a structured view of the recent literature
In order to maximize the utilization of multimodal transportation, consolidation is essential. In a consolidation system, instead of direct shipment of every cargo, low volume cargo is moved to a consolidation center and bundled into larger flows, transported by high-frequency and high-capacity multimodal services. These services have lower prices, expressed by discount factors per load unit, compared to other links.
Fig. 1 shows the variety of models being used. In practice, there are various transportation network topologies: direct link, corridor, hub-and-spoke, connected hubs, static routes, and dynamic routes (Woxenius, 2007). In the literature, consolidation systems are mostly configured as hub-and-spoke networks, with hub being a freight handling (consolidation) facility. Locations of hubs are determined and spoke nodes are allocated to the hubs. These problems are called hub location problems. Fig. 1 clearly reveals that the literature is concentrated on studying hub-and-spoke types of networks. No work is found on other network topologies. Depending on the real-world application, studying and comparing the various network topologies is interesting (Fig. 2), both from theory and an application point of view. For instance, in transportation systems with waterways, the corridor topology seems promising.