摘要

Vehicle heterogeneity and backhaul mixed-load problems are often studied separately in existing literature. This paper aims to solve a type of vehicle routing problem by simultaneously considering fleet heterogeneity, backhaul mixed-loads, and time windows. The goal is to determine the vehicle types, the fleet size, and the travel routes such that the total service cost is minimized. We propose a multi-attribute Label-based Ant Colony System (LACS) algorithm to tackle this complex optimization problem. The multi attribute labeling technique enables us to characterize the customer demand, the vehicle states, and the route options. The features of the ant colony system include swarm intelligence and searching robustness. A variety of benchmark instances are used to demonstrate the computational advantage and the global optimality of the LACS algorithm. We also implemented the proposed algorithm in a real-world environment by solving an 84-node postal shuttle service problem for China Post Office in Guangzhou. The results show that a heterogeneous fleet is preferred to a homogenous fleet as it generates more cost savings under variable customer demands.