Geoscience Reference
In-Depth Information
12.4.5
Dynamic and Multi-modal Models
One common feature of real applications is the dynamic nature of the problem.
Parameters such as costs, demand, and resources often vary over the planning
horizon. From the location point of view this gives rise to different types of multi-
period, or dynamic problems. In this type of problems, not only a routing plan has to
be made, but the times at which facilities are opened or closed must be determined.
Campbell (
1990
) develops a continuous approximation model to locate trans-
portation terminals (hubs) for a general freight carrier serving an increasing demand
in a fixed region. It can be seen as a continuous dynamic hub location model in
which it is assumed that the O/D points are scattered randomly over the service
region. Contreras et al. (
2011c
) studies a dynamic model with multiple assignments
which includes strategic decisions related to the location, operation and closing
of hub facilities over time. It is assumed that the forecast demand between O/D
pairs is known with certainty but varies over the time horizon. Moreover, the
proposed model allows hubs to be opened and closed at different time periods to
provide a flexible hub network. Gelareh (
2008
) presents another multi-period hub
location model arising in the design of public transportation networks in which it
is relaxed the full interconnection assumption and thus, additional hub arc selection
are considered.
Another important feature in some applications is the presence of strategic
decisions related to the choice for mode of transportation. Most HLPs consider
only one mode of transportation is available and thus, only one type of hub
facility. However, global hub networks usually employ a mixture of air, ground
and water transportation modes. In a multi-modal hub network, each mode can be
characterized by its flow cost structure, modal connectivity, availability of transfer
points, and service time performance.
Racunica and Wynter (
2005
) address the design of hub networks for inter-modal
freight transport on dedicated or semi-dedicated freight rail lines which could make
use of shuttle trains on the hub arcs. Groothedde et al. (
2005
) develop a multi-modal
hub location model that focus on the design of a collaborative hub network for the
distribution of fast moving consumer goods using a combination of trucking and
inland barges. Ishfaq and Sox (
2011
) present a multiple allocation model to design
a rail-road inter-modal network. It considers the location of two different types
of hubs with different modal connectivity costs and the incorporation of service
time requirements. Meng and Wang (
2011
) study the design of an inter-modal
hub network for multi-type container transportation with multiple stakeholders: the
network planner, carriers, hub operations and inter-modal operators. The proposed
model incorporates the user equilibrium behavior of inter-modal operators in route
choice. Alumur et al. (
2012a
) introduce a more general hub network design problem
in which the full interconnection of hubs assumption is relaxed and hub arc
location decisions, that include the selection of the type of transportation mode, are
considered. This model incorporates set-up costs, transportation costs and service
levels when designing the multi-modal hub network. Alumur et al. (
2012c
) study
