Transshipment and time windows in vehicle routing

Transshipment problems and vehicle routing problems with time windows (VRPTW) are common network flow problems and well studied. Combinations of both are known as intermodal transportation problems. This concept describes some real world transportation problems more precisely and can lead to better solutions. But they are examined rarely as mathematical optimization problems. In this paper two approaches are developed for this kind of merged problems. The source for our considerations is the pickup and delivery problem with time windows as a generalization of the VRPTW. This is extended by transshipment. Thereby loads can be transported by different vehicles on their path from origin to destination. A column generation technique is proposed for solving this problem.