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Comment by tunesmith | Hacker News Reader

With multiple lines, there's also the excellent visual cue to managers - if the average line length appears too long, you know you need additional cashiers. And my local grocery store is excellent about bringing in additional cashiers if any of the lines are two deep or more.

With a global line, the length of the line isn't a good visual indicator of needing more cashiers. I suppose you could just periodically count the line length, and count the cashiers, and divide, but it's not a quick eye check anymore.

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In the airports line to the passport control is usually global and formed into a switchback pattern by belt barriers. Sometimes out of boredom I measure the time it takes me to go one full section and multiply by the number of sections in front of me. Turns out to be a very good approximation of a total waiting time.

A global line solves another problem: with multiple lines, when additional cashiers are added, it tends to be the people at the back of the current lines move their way into the front positions of the newly opened lines.

It happens this way because people who are further in the line are generally “in the channel” and can’t slip out as easily... at least in grocery stores.

I was at a severely overloaded grocery store pre-storm this past weekend, which had implemented two global queues (one for 20 items or less, one for everyone else) in order to attempt to increase throughput and block the store less.

The manager was actually going around asking people at the front of the line the time they got in line, in order to be able to measure time in queue. Didn't really matter, as they had every lane open already, but seemed like a way for the manager to know if more lanes were needed.

Or they just mark the line with "one cashier reasonable wait time" and "two cashier reasonable wait time" marks, and then add a cashier whenever the line is past the mark.

Global line length is no different than average line length of multiple lines.

On a global average that is probably true. On an individual/personal level it is not. I take a strategic approach, there might be twice as many people in one line but it will be faster. No one in that line is breaking out the check book. They won't be arguing about a 25 cent coupon that expired. On the plus side I've noticed less places accepting checks. Personally I think they should be banned for basic consumer shopping entirely. Unless it is 4 digits, use a card or cash.

As for self checkout lines there should be a huge sign that asks "are you prepared for this technology?, Really? Are you sure?"

It is when the number of lines (cashiers) changes.

True. You'd need to see transactions per customer-in-store or some other leveling metric...not just customer ready to pay.

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