Decision problems at container terminals

We can distinguish between three planning and control levels in making decisions to obtain an efficient terminal, namely the strategic level, the tactical level and the operational level. At the strategic level it is, for example, decided which layout, material handling equipment and ways of operation are used. The time-horizon of decisions at this level covers one to several years. These decisions lead to the definition of a set of constraints under which the decisions at the tactical and operational level have to be made.
This page gives a classification of the decision problems that arise at container terminals. Furthermore, some related literature is indicated.

Arrival of the ship

Strategic level

When a ship arrives at the port, it has to moor at the quay. For this purpose, a number of berths (i.e. place to moor) are available. The number of berths that should be available at the quay is one of the decisions that has to be made at the strategic level.

Operational level

At the operational level the allocation of a berth to the ship has to be decided on. Imai (1997) studies how to allocate berths to ships while optimising the berth utilisation. On one hand optimal berth allocation can be obtained by minimising the sum of port staying times. This leads to ships mooring at the quay according to the first come first served principle. On the other hand berths can be allocated, without consideration of ship's arrival order, by allocating ships at a berth closest by the area in the stack in which most containers for this specific ship are located. As a result, the resulting terminal utilisation will be maximal, but ship owners will be dissatisfied by the long waiting times of the ships. Consequently, a trade-off exists between the total staying time in the port and the dissatisfaction of ship owners caused by the order in which ships are berthed. The berth allocation problem could be considered as a machine scheduling problem.

Unloading and loading of the ship

Strategic level

One of the questions arising, is the determination of the type of material handling equipments which will be used for the unloading and the loading of containers from the ship. Automated and manned terminals both use quay cranes.

Tactical level

At the tactical level the number of QCs have to be determined that work simultaneously on one ship. One of the objectives is to minimise the staying time of ships at the terminal. The most general case of the crane scheduling problem, is the case in which ships arrive at different times in the port and queue for berthing space if the berths are full. The objective in this case is to serve all the ships while minimising the total delay of the ships.

Operational level

The number of import containers that has to be unloaded at the terminal is in practice usually only known shortly before the arrival of the ship. At the operational level an unloading and loading plan have to be made. The unloading plan indicates which containers should be unloaded and in which hold they are situated in the ship. Successively, these containers are unloaded. In a hold the crane driver is almost free to determine the order in which the containers are unloaded. The unloading time of a container depends on its place in the ship.
In contrast with the unloading process, there is hardly flexibility in the loading process. A good distribution of containers over the ship is necessary. At the operational level a stowage planning is made. A stowage plan indicates for each container the exact place in the ship. Containers with the same destination, category, weight, size, contents and so on, belong to the same category. Sometimes, only for each category the positions in the ship are given. Locations of containers belonging to the same category can be exchanged between containers of this category. In making the stowage planning attention should be paid to the order in which containers need to be unloaded. Unnecessary moves should be avoided by placing containers designated for a terminal visited later during the journey on top of containers designated for the earlier visited terminals.

Transport of containers from ship to stack and vice versa

Strategic level

In designing a terminal, one of the decisions at the strategic level concerns the type of material handling equipment, that takes care of the transport of containers.

Tactical level

After the decision which system will be used has been made, one of the problems at the tactical level that has to be solved is the determination of the necessary number of transport vehicles to transport all containers in time.

Operational level

At the operational level it should be decided which vehicle transports which container and which route is chosen. Objectives are, for example, to minimise empty-travel distances, to minimise the delay of the ship or to minimise the total travel time of the vehicles.

Stacking of containers

Strategic level

A decision at the strategic level that has to be made, is choosing the type of material handling equipment that will take care of the storage and retrieval of containers in and from the stack.

The efficiency of stacking depends among other things on the stack height and strategies for storage and retrieval planning of import and export containers. Consequences of higher stacking are a higher number of reshuffles/rehandles. To reach a specific container it can be necessary to rehandle containers that are placed on top of the demanded container. To minimise delay by removing containers, reshuffling of the stack can be done in advance. On the other hand, the higher the stacking the less ground space is needed for the same number of containers. Obviously, one of the problems at the strategic level is to determine a good stack layout.

Tactical level

At the tactical level the number of transfer cranes has to be determined necessary to ensure an efficient storage and retrieval process.

Operational level

If straddle carriers take care of the storage and retrieval of containers from the stack, it has to be decided at the operational level how to route straddle carriers through the stack.


Another typical problem for a container terminal is that containers have to be stored and retrieved at two sides of the stack, namely seaside (to/from the ship) and landside (to/from other modalities). This can be done by the same yard crane/ASC. Some of the decisions that have to be made to ensure an efficient process are: which side has the highest priority (commonly seaside) and how long can containers wait before they are stored or retrieved.
The problem to decide which ASC carries out which job, can be examined in two ways. If every container is treated as an individual (QC asks for a specific container from the stack), then it is clear which ASC should carry out the job. However, one can also distinguish container categories in a stack. This holds especially for empty containers. Containers with, for example, the same destination, the same weight, contents and size belong to the same category.

Operational questions concerning storage planning are, for example, where is an incoming container stored, in which order are containers store, when is a container repositioned and in which way and which crane handles which container. For retrieval planning it has to be decided in which order containers are retrieved and which crane handles the request.