A new “rich” variation on the multi-objective vehicle routing problem (VRP), called the multi-tiered vehicle routing problem with global cross-docking (MTVRPGC), is introduced in this paper. With respect to previously studied VRPs, the MVRPTGC includes the following novel features: (i) segregation of facilities into different tiers that distinguish them in terms of different processing and storage capabilities, (ii) cross-docking at a pre-specified subset of facilities in the network (a feature referred to as global cross-docking), and (iii) the possibility of spill-over into subsequent planning periods of demand for facility visitation. The problem originated from a real-life application concerning the collection and delivery of pathology specimens in the transportation network of a pathology health-care service provider. Other industrial applications may, however, benefit from this type of VRP, such as mail sorting. A mixed integer linear programming (MILP) model for this VRP is proposed, and tested computationally in respect of seventeen small hypothetical test instances. A multi-objective ant colony optimisation (MACO) algorithm for solving larger real-world instances of the MTVRPGC is also proposed. The solutions returned by the MACO algorithm are compared with those achieved by the MILP in respect to sixteen instances and also compared to actual collection and delivery routes of a real pathology healthcare service provider operating in South Africa and it is found that adopting the routes suggested by the algorithm results in substantial improvements of all the objectives pursued relative to the status quo.

本文介绍了多目标车辆路由问题(VRP) 的一种新的“丰富”变体，称为具有全局交叉对接的多层车辆路由问题(MTVRPGC)。就先前研究的 VRP 而言，MVRPTGC 包括以下新功能：(i) 将设施分成不同的层，以不同的处理和存储能力区分它们，(ii) 在预先指定的设施子集中进行交叉对接在网络中（称为全局交叉对接的功能)，以及 (iii) 溢出到设施访问需求的后续规划期的可能性。该问题源于一个现实生活中的应用，该应用涉及病理医疗服务提供商的运输网络中病理标本的采集和交付。然而，其他工业应用可能会受益于这种类型的 VRP，例如邮件分拣。提出了该 VRP的混合整数线性规划(MILP) 模型，并针对 17 个小假设测试实例进行了计算测试。一种多目标蚁群优化(MACO) 算法用于解决更大的 MTVRPGC 真实世界实例。将 MACO 算法返回的解决方案与 MILP 在 16 个实例中获得的解决方案进行比较，并与在南非运营的真实病理医疗保健服务提供商的实际收集和交付路线进行比较，发现采用建议的路线该算法使所追求的所有目标相对于现状有了实质性的改进。