To Wave Or Not To Wave? Order Release Policies for Warehouses with an Automated Sorter1

Wave-based release policies are prevalent in warehouses with an automated sorter, and take different forms depending on how much waves overlap and whether the sorter is split for operating purposes. Waveless release is emerging as an alternative policy adopted by an increasing number of firms. While that new policy presents several advantages relative to waves, it also involves the possibility of gridlock at the sorter. Using an extensive dataset of detailed flow information from the warehouse of a leading US online retailer, we first develop a model with validated predictive accuracy for a warehouse operating under a waveless release policy. We then use that model to compute operational guidelines for dynamically managing the main control lever of that policy, with the goal of maximizing throughput while keeping the risk of gridlock under a specified threshold. Secondly, we leverage that model and dataset to perform through simulation a performance comparison of wave-based and waveless policies in this context. The waveless policy yields larger or equal throughput than the best performing wave-based policy with a lower gridlock probability in all scenarios considered. Waveless release policies thus appear to merit serious consideration by practitioners. Facilities using a non-overlapping wave policy should also consider overlapping waves or a split sorter policy.