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from the chaff.
A DU search for the words "occulus USPS saturday" yields more than I can conveniently go through related to the USPS. To save you the effort, though, I'll be brief and restate some of it here.
We handle a truly astonishing amount of mail each day. Even in my building, one of the smallest distribution centers in the country, our goal is to process 1,000,000 pieces or more per night for delivery the next day. During the week, this is no problem, but beginning Saturday night, we start a two-day process.
I'm going to simplify things here and leave a lot out for brevity's sake, but simply put, each letter you receive goes through several sortplans on several machines before it ever even reaches your carrier. The days of banks of people sitting at stations throwing mail into cases by hand is long past; we use a machine called a Delivery BarCode Sorter (DBCS) to automagically put all the mail into each carrier's walk sequence (their route). Each machine has 270 individual bins (stackers) or more and sorts between 30,000 and 40,000 pieces per hour, depending on the quality of the mail being run.
The mail is run in a bulk mode to put it into individual ZIP codes (one bin for all of 49009, for example; another for 49010, yet another for 49080, and so forth). This is called the "sectional center facility" operation, or SCF for short (I did this operation just this evening, actually). Once it's put into those broad ZIP ranges, the mail is run in a two-pass operation on the exact same type of machine.
The two-pass operation is why we can't get rid of Saturday delivery. When we perform this operation, the mail is run in a special sortplan that places it into sequences. These sequences have no meaning to anyone other than the machine, and it uses those sequences to put the mail into the carrier's actual route sequence during the second pass. The upshot of this is that all the mail that the carrier is to deliver the following day must be run during the first pass. Once the first pass is complete, we can only add to it before doing the second pass; once the second pass starts, it's impossible to add new mail.
Think of two decks of cards. You're going to give them to someone, but they have a condition: they want the cards given to them in ascending order, by suit. If you begin with only one deck, and you get them all ordered the way they want, when you go to try to add the second deck, you have to start the whole process over again if you want to be as fast about it as possible- it's much harder to add the second deck in manually than it is to just start over with both.
Such is the case with the mail. Once the second pass begins, if we want to add more mail, we have to start the whole first pass over again and rerun everything. Obviously, we don't want to do that, so we try to get as much mail into the first pass as we have time for (time, including the second pass).
Now enter the weekend.
Saturday night, the late shift starts the first pass operation and then sets it aside until the next day. The reason for this is that we still have Saturday collections (as well as other mail) coming in on Sunday. Some of that mail simply doesn't get to us the day it's mailed, and besides, we have two days to get two days' worth of mail done. We can do that; because we don't take collections on Sundays, we do have the time to process everything over the weekend.
Now eliminate Saturday's deliveries. Suddenly, Fridays are a lot heavier on the collection end (adding to the first pass I talked about above), but at the same time, we still have mail coming in (we get bulk mail deliveries and drop shipments from major mailers seven days a week). Now, we have to run the first pass, set it aside, reload it all into the machines the next day, run first pass again, set it aside again, and then run a third first pass, adding to the previous two days, and then run the second pass.
I forgot to mention that each sequence in the first pass is one tray, about two feet long. If there's more than that, instead of Seq. 1, Seq. 2, Seq. 3, etc., we get Seq 1., Seq. 1.5, Seq. 2, Seq 2.5, etc. The machines don't understand half-sequences; we have to keep track of those. Mail detected to be out of sequence shuts down the machine.
We simply can't process three days' worth of mail in one run; we simply do not have the time we need to do so. Some of our scheduling is very tightly tied to the train and air traffic schedules, too, so we can't just arbitrarily adjust. It just isn't possible using our methods, which are in the end actually very finely-tuned to ensure delivery and processing that is as efficient as possible. Maybe, if we had longer machines and more employees, we could consider it, but we've just gone through a huge workforce reduction. We just don't have the people we need right now, and we don't have enough carriers, either.
I hope that answers your question. If they would let me, I would take a video of all this; it's actually a lot simpler than it sounds.
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