A recent project for a large retailer in the Southwest provided a good example of how an element of cross-docking might be deployed to reduce the footprint of distribution space required, reduce order fulfillment touchpoints, and shorten the logical pathway for fulfilling orders.

Incoming shipments are anticipated through the use of advanced shipping notices (ASN’s). Stretch-wrapped pallet loads arrive via truck throughout the day. They arrive at doors designated for cross-docking. These doors were selected based upon proximity to the material handling system which takes advantage of the facility layout. Pallets are unloaded by fork truck, the stretch wrap removed, and cases manually inducted into one of several conveyor staging lanes. Each lane represents a “wave” of orders which will be processed either that day, or a specific day later in the week. When a wave is released, it moves downstream, and the individual cases are sorted to a specific shipping lane whose products are destined for a particular store. Other products from static storage positions and non-conveyables destined for the same store are consolidated at this point.

As waves are released, the staging lane becomes immediately available for a subsequent wave. Multiple waves are processed daily. Pallets arrive at the receiving docks with man-readable labels indicating the destination store and day to ship. The individual cases on each pallet are pre-labeled (pre-distribution) with a unique identifier that corresponds to the ultimate destination retail store, the SKU number, and the quantity. When the case label is scanned for the identifier, a lookup into a warehouse control system database occurs, which provides the routing instructions, ie, the correct shipping door. Again, orders can be comprised of cases that are cross-docked from the staging lanes, product stored in static storage positions, and/or non-conveyables. The sortation management system routes all conveyables in the current wave directly to the correct shipping lane.

Order fulfillment occurs in waves, due to a limited number of shipping doors. Most shipping doors are dedicated to a specific destination store, while a handful of other doors will each serve a number of smaller retail stores. This distribution center demonstrates how cross-docking products that are good candidates, can be integrated with order fulfillment of inventoried products to enhance overall distribution performance.

Next month we will look at a scalable, “out-of-the-box” cross docking system, its layout, and cost to purchase and implement. It will include conveyors, controls, and software to support a basic cross docking system. We have taken a modular approach to a systems solution that can truly be modularized. Join us.

If you started from scratch, many might simply build a cross dock facility with a much shallower depth than most warehouses. A depth of a hundred feet or so, with incoming product on one side that can be easily moved a short distance and loaded on the other side to an outbound truck. Most of us however, must deal with an existing facility, many times a large square box which is not generally the preferred layout. However, as long as the existing facility has a sufficient quantity of dock doors, yard space, and an adequate footprint, you may be fine…

Simply having a lot of dock doors does little for efficiency if the doors are located on opposite walls at a great distance from one another. Conveyor companies might love this, but there are better alternatives. Some recommend all the doors on one wall, or even at 90 degrees to one another. High speed movers would then travel between incoming and outgoing doors in closest proximity to one another. Proximity of high traffic incoming and outgoing doors is key. Distance equals costs. Many consider dedicating only a portion of their facility for cross dock duties as an acceptable workaround.

Pallet handling versus case handling create separate requirements. Congestion in dock areas will be a killer. Sufficient dock space is key to moving products quickly and safely. This is particularly true if the company is growing or deals with seasonal products. Ample space must be available for any pallet staging activities near shipping doors. If aisles are part of your logical pathways, then oversize them in high traffic areas.

One of the more complete reviews of cross dock design is by John Bartholdi and Kevin Gue in Transportation Science. They provide an analysis of the impact of “shape” on the performance of a cross dock operation. They considered a wide variety of designs and freight flow patterns, and offered the following summary:

“Shape matters. Freight must be moved across the dock and total distance traveled is a good estimate of labor costs. The best shape for small to mid-sized cross docks is a narrow rectangle or I-shape, which gets maximum use of its most central doors. For larger docks, alternative shapes are more attractive. The best shapes for larger docks will have piers branching out from a central area. These designs have more corners, for which they pay a cost. However, they achieve greater centrality, and so more distant doors are closer to other doors. For example, the T-shape is best for dock sizes between about 150 to 200 doors. For larger than 200 doors, the X-shape is best. Despite having four inside corners near the center of the dock, the worst doors are not far from the center. When freight flows are concentrated among few destinations, the point will be deferred at which a more complicated design becomes attractive. This is because the labor will be concentrated on a subset of the dock, and so the dock is, in effect, a smaller dock.”

Layouts designed on solid principles will address the “layout issue”. Although we have been focusing on the internal logistics of cross docking, we do need to make note of another obvious area of interest…. the “trailer spotting” issue. A poor spotting process defeats a quality layout. They work in concert. There are many issues you deal with in creating an optimum design for cross docking. In the next brief, we will take a look at cross docking in actual practice. This will include a couple of applications that deal with the issues we have discussed, and others. One application is complex, the other is a simple scalable system (actually including system costs).