Back when we were delivering twice daily, we were using the Letter Sorting Machine, or sorting by hand. With the development of the DBCS (Delivery BarCode Sorter), we were able to cut the second delivery without impacting overall service, because the mail was being processed so much faster.
However, to fully understand why] we can't eliminate Saturday delivery, you have to- have to- know how the mail is processed. Without going into a long explanation, each piece of mail letter mail moves through our machinery at least three times. The first run processes the mail from a raw 3-digit ZIP prefix into individual ZIP codes (a 5-digit sort). After that, the mail is run twice more, in an operation called DPS (delivery point sequence).
Once mail is run through the first pass of that two-pass process, and the second pass is started, no mail can be added. Period. We have to run what we have and get it out the door because of the way the machines do it, and this can't be changed. Once that first pass is done, that's it until the next day. Then, the second pass places the mail into the carrier's walk sequence and it's shipped out of the building. We can set aside one day's worth of mail to add to that first pass, but no more than that. Those same machines are used to perform the same 3-digit sort I spoke of above, on other shifts.
When we process mail on Saturday, we run as much as we can that night because there's no delivery the next day. This is the only day we can do that. Were we to eliminate Saturday delivery, we wouldn't have enough physical space on the machines to process all three days of it and Monday's mail would be late, which would ripple through the rest of the week.
You have to actually work in the plant, doing the operation, to fully understand why eliminating Saturday delivery just is not an option. We don't have space on the machines, in the plants, or in our delivery vehicles to deliver three days' worth of mail (Saturday, Sunday, and Monday) in one go.
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