This paper investigates a drayage problem, where a fleet of trucks must ship container loads from a port to importers and from exporters to the same port, without separating trucks and containers during customer service. We present three formulations for this problem that are valid when each truck carries one container. For the third formulation, we also assume that the arc costs are equal for all trucks, and then we prove that its continuous relaxation admits integer optimal solutions by checking that its constraint matrix is totally unimodular. Under the same hypothesis on costs, even the continuous relaxations of the first two models are proved to admit an integer optimal solution. Finally, the third model is transformed into a circulation problem, that can be solved by efficient network algorithms.

本文研究了一种拖运问题，在该问题中，一队卡车必须将集装箱货物从一个港口运送到进口商，从出口商运送到同一港口，并且在客户服务期间不将卡车和集装箱分开。我们提出了针对此问题的三种公式，这在每辆卡车运载一个集装箱时都是有效的。对于第三个公式，我们还假定所有卡车的电弧成本均相等，然后通过检查其约束矩阵是否完全为单模，证明其连续松弛允许整数最优解。在相同的成本假设下，即使前两个模型的连续松弛也被证明可以接受整数最优解。最后，第三个模型转化为流通问题，可以通过有效的网络算法解决。