Impact of cross aisles in a rectangular warehouse: A computational study

Order picking is typically the most costly operation in a warehouse, and traveling is typically the most time-consuming task within order picking. In this study, we focus on the layout design for a rectangular warehouse, a warehouse with parallel storage blocks with main aisles separating them. We specifically analyze the impact of adding cross aisles that cut storage blocks perpendicularly, which can reduce travel times during order picking by introducing flexibility in going from one main aisle to the next. We consider two types of cross aisles, those that are equally spaced (Case 1) and those that are unequally spaced (Case 2), which respectively have equal and unequal distances among them. For Case 2, we extend an earlier model and present a heuristic algorithm for finding the best distances among cross aisles. We carry out extensive computational experiments for a variety of warehouse designs. Our findings suggest that warehouse planners can obtain great traveltime savings by establishing equally spaced cross aisles, but little additional savings in unequally spaced cross aisles. We present a look-up table that provides the best number of equally spaced cross aisles when the number of cross aisles (N) and the length of the warehouse (7) are given. Finally, when the values of N and T are not known, we suggest establishing three cross aisles in a warehouse.