New benchmark instances for the inventory routing problem

The existing sets of benchmark instances for the inventory routing problem (IRP) have been beneficial for investigating and illustrating the properties of the problem. However, they possess certain features and design choices that are not necessarily representative of all real-world IRPs. Therefore, we propose a new collection of 270 real-world-like instances ranging from 10 to 200 customers. These instances vary in terms of the number of vehicles and their capacity, the length of the planning horizon, the demand structure, and the geographical distribution of customers. Transportation and inventory holding costs resemble costs found in practice. We present an instance space analysis showing that the new instances nicely complement the original instances. To derive lower and upper bounds for each instance, we present computational experiments with two high-quality solution methods: a matheuristic and an exact branch-and-cut method. The results confirm that the new set of instances is hard to solve with the proposed methods, and they demonstrate the need for developing new solution methods.