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I. Introduction
Transportation using a single mode without transfers is often perceived as the best option as cargo handling is limited to the locations of the shippers and consignees and a single transportation operator is responsible for the entire movement of cargo. However, this is often not possible as there are physical constraints, such as the land-sea and the air-land boundaries, which pose as a barrier to the flow of freight on the same mode. For example, cargo shipped on long-haul segments by sea or air has to be loaded onto trucks at the ports or airports to be delivered to the final destination. Thus, since the early days, long-distance transportation, with the exception of trucking, has always consisted of a combination of modal solutions (Batten & Thord 1989, 5). Intermodalism inherently has a disadvantage in that goods must come to a halt by virtue of interchange between modes and additional handling costs and time must be incurred at the transfer point (Mahoney 1985). Despite this disadvantage, it is apparent that intermodalism has emerged in recent decades as a viable alternative in its own right rather than simply a necessary measure to overcome physical barriers. This can be attributed to remarkable developments in the areas of transportation technology and distribution logistics which include the growing importance of non-vessel operating common carriers (NVOCCs), containerization of cargo, the proliferation of hub-and-spoke systems, and developments in information technology facilitating 'through-transportation' documentation. Movement of cargo using two or more modes can now take place though it is in a continuous flow from origin to destination under a single rate, reflected in through-billing and through-liability for the entire journey (Hayuth 1987, 15). Intermodal transportation is currently used as a strategic tool to harness the advantages of different modes of transportation. The difficulties associated with different conditions of carriage as well as physical transfer in intermodal transportation have become gradually insignificant relative to the benefits to be derived in terms of cost, transit time, routing flexibility, service availability and reliability.
Of the various intermodal combinations, the one which has received relatively very little attention is sea-air transportation. Although this form of intermodal transportation has existed since the 1960s, it is only in the past decade that this option has captured...