No abstract

Within both retail distribution and less-than-truckload transportation networks crossdocks vary greatly in shape. Docks in the shape of an I, L, or T are most common, but unusual ones may be found, including those in the shape of a U, H, or E. Is there a best shape? We show that the answer depends on the size of the facility and on the pattern of freight flows inside. Our results suggest that many large crossdocks in practice suffer from poor design that increases labor costs on the dock.

Supervisors in a less-than-truckload freight terminal establish material flows inside the terminal by assigning incoming trailers to open doors. A common scheduling strategy is to look ahead into the queue of incoming trailers and assign them to doors to minimize worker travel. We develop a model of the resulting material flows and use it to construct layouts that exploit this type of scheduling policy. Based on data from a test site, our results suggest that look-ahead scheduling alone can reduce labor costs due to travel by 15-20% compared to a first-come-firstserved policy. Layouts constructed with the material flow model provide further savings of 3-30% in labor cost due to travel, depending on the mix of freight on incoming trailers and the length of the queue of trailers from which the supervisor makes assignments.

Handling freight in a crossdocking terminal is labor intensive and therefore costly because workers must unload, sort, and transfer a wide variety of freight from incoming to outgoing trailers. The e ciency of workers depends in large part on how trailers are assigned to doors around the dock; that is, on its layout. A good layout reduces travel distances without creating congestion, but until now no tools have been available to construct such layouts. We describe models of travel cost and three types of congestion typically experienced in crossdocking terminals, and we use them to construct layouts that minimize the labor cost of transferring freight. We report on the use of our models in the less-than-truckload trucking industry, including an implementation at a terminal in Stockton, California that improved productivity by more than 11%.

The cost and service performance of an order fulfillment center are determined partly by how workers are organized into an order picking system. One common approach is batch picking, in which workers circumnavigate a picking area with other workers, gathering items on a pick list. In some systems with high space utilization, narrow aisles prohibit workers from passing one another when in the same aisle, and this leads to congestion. We build analytical and simulation models of these systems to investigate their behavior under different levels of activity. Among other things, our results suggest that when the system is busier and pick density is high -that is, when workers stop often to make picks -congestion is less of a problem and workers are more productive.