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.