MethodologyThe choice of transport

Methodology
The choice of transport mode or combination of transport modes has a direct
impact on the efficiency of a multimodal transport system. Depending on the
mode chosen (Liberatore and Miller, 1995), the overall performance of the
multimodal transport system will be affected. Simple cost-distance models of
road versus rail are commonly found (Fowkes et al., 1989; Hayuth, 1992;
Marlow and Boerne, 1992) for national movements or sea versus air (Hayuth,
1986; Jung, 1994) over longer, intercontinental routes. As the multimodal choice
is of vital importance to the success of international trade, various models have
also been created (Beresford and Dubey, 1990; Beresford, 1999; Minh, 1991;
Barnhart and Ratliff, 1993; Yan et al., 1995) to aid transport decision makers in
choosing the most effective transport mode or combination of transport modes
that not only minimises cost and risk, but also satisfies various on-time service
requirements.
The cost model, which is presented here, includes both transport (road, rail,
inland waterway, sea) and intermodal transfer (ports, railfreight terminals,
inland clearance depots) as cost components. This model has been adapted
from Beresford and Dubey (1990) and improved by Beresford in 1999. The
model may be considered in four developmental stages from its basic form
(Figure 1(a)) through two intermediate stages (Figure 1(b) and 1(c)) to its final
mature form (Figure 1(d)).
The model assumptions are based on the premise that unit costs of transport
vary between modes, with the steepness of the cost curves reflecting the fact
that, for volume movements, sea transport should be the cheapest per tonnekm,
road transport should normally be the most expensive (at least over a
certain distance), and waterway and rail costs should be intermediate. At ports
and inland terminals, a freight handling charge is levied without any material
progress being made along the supply chain; a vertical ``step’’ in the cost curve
therefore represents the costs incurred here. The height of the step is
proportionate to the level of the charge. Depending on the route chosen, the
combination ofmodes and cost will be different. The purpose is to find the most
competitive route cost wise. The model may also be used as a contributory tool
in the debate over the value of time in freight transport operations. Although
this approach in itself is not new (Levander, 1993; Christopher, 1998), the
portrayal of the cost components as increments along the transport chain is
quite novel.