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Comment by defertoreptar | Hacker News Reader

It's true, but there are two things to factor in:

1) People tend to sort themselves by picking the shortest line.

2) Grocery stores try to staff only just enough registers so that no register ever has a gap.

If you combine those two things, the efficiency closes in on what a global queue would. My main gripe is the "unlucky" factor where the shopper gets stuck behind a very slow person, which the global queue would fix.

The third, dark-patterny part of this is how grocers benefit from people and their children being stuck next to impulse merchandise while they wait.

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My local cinema concession stand moved from a single queue to one queue per register. The variance increased noticeably every time I have visited since and all the staff I have spoken to hated the change and said they were regularly getting complaints about it. When I asked why they changed I was told one of the managers did it because it made the lines shorter and they concluded that meant the wait must also be shorter.

Maybe purchasing a text book on Queueing theory and giving it to one of the staff would help, topics that dense tend to change minds quickly when they are disseminated at high velocity toward management.

You may read that as you please.

Flips to a page with a formula using sigma notation

"This isn't rocket science bro. Obviously more lines = faster."

You're not factoring the perception of the multiple shorter lines vs a long line. It's can be the difference between someone glancing who might/might not want popcorn and jumping in line (which ends up taking longer, but they're already committed) vs looking at a single LONG line, and deciding not to bother.

A Whole Foods near me used to have a system with a global queue, where you would sort into multiple lines (e.g. A, B, C, D) and there would be a screen saying which line's turn it was to send someone (A first, then B, then C, then D, rinse and repeat). It was pretty quick and nobody seemed to mind it much

You can have your cake and eat it too, it turns out.

Fry’s does the same thing with the screen (used to have a human for it), with a single global queue.

Same thing; never had a concern with it. But whole foods and fry’s are bigger and I end up spending a good deal of time there just shopping uaually, so queue length isn’t as concerning as when I’m in a smaller grocery, just grabbing a gallon of milk

The problem I noticed with the system like this is that cashier is idling for a bit while the next customer walks from the head of single line to the specific register. Depending on the layout this can be a significant distance. There’s no such idling in multiple lines.

That is why some places started to use hybrid system. One single line until very end where someone marshals you at the end of many very short lines.

I should be clear; there are actually multiple lines and multiple registers. It's just that no line corresponds to a specific register.

Imagine four lines arranged next to each other, at the head of eight registers arranged similarly to a self-checkout area. There will always be four people at the head of the lines. The first person in the first line gets to go, then the first person in the second line, then the first person in the third line, then the first person in the fourth line, and then it cycles back.

Because in practice it is extremely rare for four out of eight registers to simultaneously open up, the next person is always at the front of their line already, which avoids this particular travel distance problem.

I also regularly go to a Whole Foods with this system, it initially felt like a good compromise between "one slow cashier shouldn't hang up a lot of people" and "people react negatively to long lines, even if they're fast-moving".

The way this particular one works is with color codes -- there are four color-coded lanes, and when a cashier becomes available, they are announced by the system, which cycles through the colors.

It has some failure modes.

In the "dilute limit", if a customer approaches the lines and there's nobody else there, there's no indication of which color was last called or which is next, so they have to guess. If they guess wrong and someone else shows up and guesses right before a cashier becomes available, they might lose out. This effect goes away once the system acquires "memory", by having people in the queue who have seen the last cashier announcement.

At moderate congestion, it can be hard to assess which lane is shortest, because people don't space themselves evenly, and sometimes go up in groups. People have a pretty strong sense of fair play, and I've seen people grumbling when the system breaks the expected FIFO dynamic.

But, generally speaking, it works better than I thought it would when they first set it up.

I should be clear and say that the Whole Foods I was at used this color scheme; I just used letters for illustrative purposes :)

The Whole Foods that I live near now uses a single line heading to multiple express registers, as well as traditional checkouts. This seems to be the worst of both worlds; not only can I not tell which traditional checkout will finish first, I also can't really tell how long the single express queue is actually moving! Are registers opening up at a regular pace or are they opening in waves? It's honestly the worst.

I had an awful experience with this system the last time I went to a Whole Foods. The problem was that there was insufficient signage explaining the system, and the computer announcer was quite vague about who should go up. When a register was free, the computer spoke “next”, not “A” or “D”; if there was a screen with the letter, it wasn’t easily visible. In fact, I didn’t even notice the tiny signs labeling each line while I was standing in line.

As a result, when I was at the front of line “A” and the computer called “next” after the other lines had gone, I went forward, but another customer did too. The other customer ended up cussing me out for going ahead of him – it turned out he was in a “D” line that, from my “A” line, looked like part of the “C” line. Being yelled at for not understanding the rules of a poorly explained system made for a unpleasant experience.

A German chain for electric goods (Saturn) switched to a global queue recently (the first person in the queue gets called to the next available register). I find it a much better customer experience.

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.

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.

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.

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

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?"

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.

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

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.

Trader Joe's uses a single line (in every one I've ever been to) and it is wonderful. Even a line wrapping the entire store will only take 10-15 minutes because they staff appropriately and you're almost always moving.

You also are always next to some kind of food item and the impulse buys are staged in an even longer display than in a regular grocery store. Instead of four feet wide and five feet tall, it may be 20-30 feet wide and 3-4 feet tall.

> Trader Joe's uses a single line (in every one I've ever been to)

Multiple lines in western Washington, FWIW.

My Tj's has a single line at the front of the store (likely optimized for those taking public transport and purchasing fewer groceries). But in the back, where the parking lot is, it's a queue per register.

Phoenix area TJ's use multiple lines

Multiple lines at Trader Joes in Westwood LA.

Multiple lines in Oregon.

I’ve never seen a single line TJs. And that’s across four States.

Same. VA / WI

If you're ever in downtown San Francisco, half the TJ store is the line when it's a little crowded!

It's absurd. Works pretty well though!

For the record, it's the only TJ's in SF that does this. And I agree, it works well given how much traffic it gets.

Same design in the downtown Boston branch. Line snakes through entire store with lots of opportunity to pick up things along the way.

It might be a SF thing or downtown thing, where there isn’t room for multiple lines.

None of the other SF stores are single line.

The ones I'm referring to are in Manhattan and Philadelphia.

>My main gripe is the "unlucky" factor where the shopper gets stuck behind a very slow person, which the global queue would fix.

Yeah, but that’s one important metric you should judge a queuing system by: standard deviation of wait time. It means entrants are less able to allocate their own time, since they have to anticipate higher variance.

In fact that's not how supermarkets evaluate queuing. They evaluate strategies based on exposing you to the most items while waiting - or you can check yourself out for the "discount" of not being exposed to impulse items.

Target did a trial of a global queue in a store near me, it lasted about a year.

I had a family member that worked at Target, and I asked about why they have 40ish registers, but normally only <10 of them are open. It's all about the holiday shopping. Those ~8 weeks see so much traffic it is worth the "wasted" square footage in the store the other 10 months of the year.

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