Reader Question

To reduce distribution costs, we are evaluating whether we can reduce the number of sort lanes we use. Currently, we have 10 diverts, and 4 to 5 operators move between them to palletize cartons coming off the sorter.

The travel time moving between the diverts might be reduced by reducing the number of divert lanes we actually use.

How should we think about this?

Industrial Engineer
Large Wholesale Distributor

Category: Material Handling


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Expert Panelist Response: Cliff Holste, SCDigest’s Materials Handling Editor

In follow-up email discussions with this reader, we learned a few more facts: (1) the divert assignments are sorted by carrier; (2) the volumes per carrier/divert vary substantially, with the largest carrier/divert volumes being about 10 times the smallest carrier/divert volumes; (3) the company does not process a lot of waves/pallets - for larger customers, a pallet may be closed relatively quickly, but for other customers, a pallet may be open until it is closed at the end of the shift; (4) the company currently uses about 10 pallet positions per divert – to reduce diverts used, the number of pallet positions per divert would naturally need to be increased.

This is an interesting and, in a sense, complicated question, but we will do our best here in the space we have.

The question naturally brings up the issue of how many diverts and pallet positions per divert a company needs or should have to begin with.

The number of diverts is based on several factors, such as:

  • Number of orders per batch
  • Number of batches per day
  • Number of pallets per order
  • Number of cases per order

In addition to the above, you have to factor in the rate at which you can manually sort and palletize cases at the end of a divert lane. If you have just one pallet position, that rate would be much higher than if you have to scan and sort to 10 pallet positions.

If you did not have to sort, you should be able to palletize 5 to 6 cases per minute (CPM). This company has an average ship rate of 15 CPM. So, they would need 3 people if no or very little sorting was involved.

This company currently uses 4 to 5 people to scan/sort/palletize to 10 pallets per lane. Reducing the number of lanes by increasing the manual sorts per lane is unlikely, I believe, to improve productivity, as the sorting/travel time to an increased number of pallet positions will largely erode any savings from reduced travel between diverts.

To make another general point, most sorting systems are located on or in close proximity to the shipping dock, where floor space is at a premium.  So, if you are considering manually sorting to multiple pallet locations off the end of each sort line, you must take into consideration not only the floor space required to lay down each pallet position, but also the replenishment of empty pallets, and lift truck access aisles for removal of completed pallets.

There are also safety issues involved with lift trucks and people sharing the same space. As this arrangement begins to spread out to say 20 feet between each sort line, the cost of the sorter increases along with the cost of the recirculation conveyor. These additional costs have a very poor ROI, in my experience.

Here are some options for this company and others to consider:

(1) Reducing manual scanning and sorting may be the best way for them to increase productivity. An approach I will call the primary/secondary sort will do that the best – and it looks like their sorter has the capacity to handle it. It is most applicable for operations with medium volumes of cases.

Given 10 order consolidation lanes, the Primary Sort would include a pick batch of 100 orders (10 per lane). Orders 1 thru 10 - sorted into lane #1. Orders 11 thru 20 – sorted into lane #2, etc. The WMS should be able to allocate the 100 orders across the 10 lanes so that total quantity of cases assigned to each lane is about the same.  At the end of each lane, all of the cases for the 10 orders will be stacked on a pallet(s) – no manual scanning or sorting required. When a Primary pallet is full, a flag is attached to it that IDs the lane number, and the pallet is removed to a staging area.

When the Primary Sort operation is completed, the Secondary Sort operation can begin.

The cases on Primary Pallet(s) for (Lane #1) are placed back onto the sorting system.  This time the cases are discrete sorted by customer order into lanes 1 thru 10.

At the end of each lane, the cases are palletized onto their customer specific pallet – no manual scanning or sorting required.  Sorting for Primary Pallets for Lane #2 can begin as soon as palletizing for Lane #1 is completed.

With the addition of a little system sophistication, overlap time between sorting operations can be minimized.

The double handling of cases, inherent in a Primary/Secondary Sort Operation, should be more than offset by the efficiencies gained in picking a larger batch of orders and the elimination of the manual scanning and sorting of cases. Another benefit may be in reducing errors that typically occur in manual sort-to-pallet operations.

There would be no physical changes required to the existing system layout, just software and operational changes.

This company would have to do a comparative productivity analysis of current versus this method to see if there is any justifiable improvement for making the change.

This approach is not new or all that unique. I know, for example, that McKesson’s has been using Primary/Secondary sorting for many years for their batch pick/sort-by-route shipping operations.

(2) Another option is to look at re-using pallet positions during or across waves. So, rather than increasing the number of pallet positions per divert, which decreases productivity and can increase errors, when a pallet is full, it is closed and another pallet for that customer (or a different customer) is opened in its spot in mid-wave.

This is the approach Doug Baker and totes Isotoner wound up taking in their sortation system, though their volumes are much higher and pallet positions are good for one wave only (I designed this system).

Initially, we had the WMS “pre-build” the pallets, and the total system (WMS and WCS) did support dynamic waves (more than one wave being handled on the pallet positions). But, if a pallet was missing a carton, it was cumbersome to close the pallet and send it to a holding area for the missing carton(s).

So, Baker decided to kill the WMS carton building and let the operators build and close the pallets. This does seem to improve total system productivity, but the “price” is that for multi-pallet orders, it is more likely that SKU integrity will be lost. Before, the WMS to the extent possible ensured that all cartons of a given SKU were on the same pallet, unless there was not an alternative. With the operator driving the pallet build, it is more likely a SKU could be spread across pallets.

(3) Another approach exists for this or other companies that does require some physical changes. That would be to incorporate a continuous re-circulating loop (“Poor Man’s Sorter”) to handle medium to small orders. The loop would be fed from the existing sorter. Large orders would be sorted down 2 or 3 of the existing lines to palletizing.

(4) Finally, another alternative would be to increase the number of sort lanes spaced in side-by-side pairs 12 feet apart and reduce the manual sorting per lane to 4 or 6 pallets. This will increase productivity, reduce errors, and conserve floor space.  Another benefit is that the additional sort lines provide an additional accumulation buffer, which increases system efficiency.

There are many tradeoffs and the right solution depends on doing an analysis of equipment cost, space, labor, safety, and productivity/ROI.

That’s about as much as we can handle in this forum. If any of you would like to discuss a related or any material handling challenge, please send me a note at

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