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Optimizing the door assignment in LTL-terminals (Stiftung Industrieforschung)

Background

LTL-terminals are transshipment points for road freight traffic. Trucks are unloaded at a door they are assigned to, their cargo is sorted and loaded into trucks waiting at other doors. Several operational, tactical and strategic planning issues arise in the context of LTL-terminals. Three of them have been considered in this research project, which was funded by the Deutsche Industriestiftung:

• Choice of door functions for incoming and outgoing traffic (tactical)

• Allocation of short-distance and long haul traffic to the doors for outgoing traffic (tactical)

• Allocation of incoming trucks to doors including time-windows (operational)

The objective of the project was the minimization of internal costs due to unloading and loading actions and the necessary internal transports. Moreover, waiting and handling times may not exceed particular amounts of time. Currently, this problem is solved mainly based on the experience of the scheduler.

Approach

In order to achieve a general method for solving the aforementioned problems, a case study with a particular LTL-terminal was considered. The information gathered from visits and discussions with the persons in charge were mapped into a mathematical optimization model with material-flows and time slices. A column generation method, i.e. a special kind of decomposition method for that kind of flow problems, was used to find heuristic solutions which turned out to be very successful for the planning issues. The algorithms were implemented into software which can easily be handled by the scheduler. He can create a whole plan from scratch and adapt it with regard to his own experience.

Results

The software described above is a useful prototype for showing the advantages of mathematically based planning assistance. The possibility to change planning details manually increases the acceptance of experienced users.

Contact: Prof. Dr.-Ing. Uwe Clausen