7 Conclusions and future research opportunities
B2C e-commerce sales are increasing every year. Customers expect a fast and accurate delivery. In order to fulfill these high customer expectations all supply chain functions have to be optimized simultaneously. In this paper, an order picking process and a vehicle routing problem are integrated into a single optimization problem, i.e., an integrated order picking-vehicle routing problem (OP-VRP), in a B2C e-commerce context. As in the literature, most integrated problems consider a production environment, first production scheduling and order picking processes are compared before an integrated OP-VRP is formulated. In general, different terminologies are used to define rather similar concepts. The related concepts are linked with each other. For instance, batching and zoning in a warehouse context are related with corresponding processes in a production environment. In both a production context and a warehouse, processed goods need to be delivered to customers. Consequently, there are interdependencies between production and distribution as well as between warehousing and distribution. According to the authors, it is the first time order picking and vehicle routing decisions are integrated. Mathematical formulations for a single order picking problem, a vehicle routing problem with time windows and release dates, and an integrated problem are presented. The performance of the proposed integrated OPVRP is compared to an uncoordinated approach in which first an OPP is solved and afterwards a VRP. The total costs obtained by using an uncoordinated approach are compared to the total costs obtained by using the integrated approach.
