Two-stage sort planning for express parcel delivery

The design and control of effective sortation systems has become more complex as both the volume parcels also number time-definite service options offered by parcel carriers have grown. In this article, we describe approaches for planning two-stage sort operations that explicitly consider time deadlines sorting capacities. sorting, are sorted into groups a primary sorter then from these dispatched to secondary stations final sort. We define optimization problem in setting using mixed-integer programming, where objective is minimize operational cost subject machine capacity deadline constraints. Since detailed based on flows time–space network difficult solve realistically-sized instances, develop an alternative formulation easier shares same feasible region first-stage decisions with model; many practical functions, simpler model can be used find cost-optimal solutions model. illustrate proposed modeling approach its effectiveness real-world instances obtained large express provider.