Modern inventory systems, such as those in mail-order and e-commerce warehouses, airport luggage systems, and custom-order manufacturing facilities, face significant challenges in providing fast, accurate responses to requests for inventory items. Delays and backlogs in the process of responding to such inventory requests can result in reduced worker productivity, order cancellations, reduced throughput, or other losses. In recent years, automation has improved the speed and efficiency of storing and retrieving inventory items within such systems. Nonetheless, in high volume systems, the speed and efficiency of automated systems may still limit the overall effectiveness of automated systems.