Task Interleaving

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Published October 21, 2003

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Reducing costs in your distribution centers is always a top priority. If your pallet-handling equipment and operators are moving “empty-handed” from one task to the next, you should explore task interleaving as an opportunity to increase efficiency and reduce costs for labor, equipment and maintenance. Task interleaving is a well-established industry best practice. It uses the warehouse management system (WMS) to assign tasks to workers in ways that make use of each trip that they and their associated equipment make during their work shifts. For example, a fork truck operator who is delivering a pallet for outbound staging may be directed to pick up an inbound pallet on the dock and move it to reserve storage before going to pick up the next outbound pallet. The greatest benefit of this practice is that it typically can eliminate 25 percent to 30 percent of the machine travel associated with pallet moves. When explained, the simplicity of the task-interleaving concept is obvious-don’t waste time and motion-but implementing it successfully requires modern technology and a thorough understanding of your operations. Task interleaving uses your WMS to try to make every trip count for equipment and people, but the capabilities of technology and the understanding and insight of people must combine to think fast enough and smart enough to really make it work.

Inbound and Outbound: Finding the Sweet Spot

Task interleaving can reduce demand for labor and equipment, but it is not a one-size-fits-all solution. This tactic is most beneficial when used in operations with a relatively high volume of product moving in and out of the facility at the same time in full-pallet quantities. This scenario is typical for operations such as retailers that have high-volume seasonal requirements where products are received and shipped in full pallet quantities, or where receiving and shipping are physically located close to each other. Not all tasks should be interleaved; the location of the operators, the type of equipment and the priority of the tasks must be factored into the decision formula. A few that generally work are pallet putaway and pallet pulling, pallet putaway and pallet replenishment, pallet replenishment and pallet pulling, location cycle counting and order pulling, and, if inspection is not required, unloading and putaway. In general, truck loading and unloading, as well as piece and case picking due to their equipment and isolated work areas can be interleaved. Every distribution center, however, has unique requirements and operations that must be reviewed prior to interleaving or ruling out interleaving of operations. Because it eliminates or greatly reduces deadheading, interleaving inbound and outbound tasks for operators greatly reduces unproductive travel time from location to location. Here are some major considerations in deciding if task interleaving can work for you. The Right WMS: A critical requirement for successful task interleaving is having a WMS that can support it while ensuring that high-priority tasks get completed on time. It’s a balancing act-efficiency vs. urgency. The Right Tasks: Having a good balance of complementary tasks is another key requirement for effective task interleaving. Pallet moves to and from the dock are good examples of complementary tasks. Task interleaving is especially beneficial for tasks with the following characteristics:

  • The same type of equipment can be used to perform both types of moves.
  • The drop point for one type of move is relatively close to the pick-up point for the other move.
  • There are fairly equal numbers of each type of move.
  • Matching the proper tasks also plays a key role in being able to task interleave successfully. For example, pairing putaway tasks with replenishment tasks is usually a bad idea. The drop-off and pick-up points are seldom close to one another, the task priorities are typically not well aligned, and the frequency of these tasks typically varies greatly. Companies need to do a good job of identifying the tasks that should be paired for interleaving on specific job codes in the WMS.

The Right Staffing: Balancing resources across job codes based on work volume is important to a successful interleaving program. Improper staffing will get task queues out of balance, which results in priority exceptions and, ultimately, zone-skipping. Once a facility begins operating in an exception mode, the WMS overrides task interleaving and efficiency gains evaporate. Companies should consider developing a standard staff planning and allocation strategy as well as a process for implementing it. Having the right labor management system (LMS) in place will give you performance management capabilities to improve productivity and the staff planning tools to achieve a balanced workforce.

Juggling and Judgment Skills Are Essential

Managing work queues and managing task priorities are two of the most important factors that drive success in task interleaving. More attempts at task interleaving fail due to poor priority management and poor work queue management than for any other reasons. Task priorities within the system must be consistent with the actual priority of the task. For example, if Task A is for a fluid load order that needs to ship in two hours and Task B is for a staged load order that needs to ship in six hours, Task A truly has a higher priority than Task B. However, if both Task A and Task B are released into the work queue at close to the same time and if the system sets their priorities equal to one another, the chances of successfully using task interleaving go down significantly. Because the system believes the task priorities are equal, there is too high a probability Task B will be completed prior to Task A. As more and more events like this occur, priorities get further and further out of balance, and operators are forced to override task interleaving in order to meet service levels. Efficiency gains are lost. The most successful task interleaving depends on a balancing act involving the number and kinds of tasks in the WMS work queue. Opportunities to interleaf tasks will be greatest when the work queue is full enough to keep all hands busy and when it holds as many tasks as possible that are amenable to task interleaving. Filling the work queue until it “spills over” is not the right approach, and quantity is not the same as quality when you are looking for interleaving opportunities. A practice that has a devastating impact on task interleaving is flooding the WMS work queue with future work. Putting work into the active queue too early results in an imbalance of task priorities. Similar tasks enter the work queue with the same priority even though, as illustrated in the example above, the required completion time is what determines the true priority of a task. Doing tasks too early leads to a scramble to catch up on more important tasks, imbalances result, exceptions become the rule, and benefits evaporate again. Releasing work into the active work queue too late can also have a devastating impact on task interleaving, too. By the nature of task interleaving, the total work hours invested to complete a day’s work are reduced, but the time to complete a unit of work (say, an outbound order) is often increased. If a unit of work that used to be completed in two hours without interleaving takes three hours with interleaving, the tasks that make up that unit of work need to be released at least three hours prior to the required completion time. If that does not happen, the operation yet again is forced to process exceptions in order to meet required service levels.

What Will Work for You?

As you can see, task interleaving requires a thorough understanding of your distribution center operation’s work tasks and the capabilities of your WMS. It requires the right opportunity-and the expertise to configure and implement the process correctly. The potential benefits make it well worth exploring. Tompkins International knows operations and understands every major WMS in use today. We’re ready to help.

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