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.
You may read that as you please.
"This isn't rocket science bro. Obviously more lines = faster."
You can have your cake and eat it too, it turns out.
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
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.
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.
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.
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.
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.
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.
Multiple lines in western Washington, FWIW.
It's absurd. Works pretty well though!
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.
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.
As for self checkout lines there should be a huge sign that asks "are you prepared for this technology?, Really? Are you sure?"
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.
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.
My favorite solution is that adopted by my local Trader Joe's. They use local queues, but somehow seem to magically always have just enough checkouts open that at most one person is waiting in each queue. Further, the queues are not separated from each other by barriers, so when a cashier empties their queue (a common occurrence), they can steal customers from neighboring queues.
In fact this system works so well that I don't think I've ever had to finish waiting for the person ahead of me in my chosen queue. Almost invariably, either there is a free register, or another cashier steals me before I reach the head of my queue.
I think this system is enabled partly by the fact that Trader Joe's are almost always small enough that workers can be summoned to cashier duty from anywhere in the store in a matter of seconds. Traditional supermarkets are too large to be able to react so quickly to workload variance, leading them to rely on deep queues to keep cashiers busy.
(Not all Trader Joe's are blessed with this system. There is one in Boston, the smallest TJ's in the nation, which, owing to its size, must resort to a global queue which, at peak hours, snakes its way through all aisles of the store such that the only means of shopping is to first get in the checkout line, and then to add things to your basket as you slowly make your way to the checkout. I suppose in some sardonic sense this is the most efficient of all systems, if you are purchasing items from all sections of the store anyway.)
In the real world you won't have the same service time for both cases since you need to add in walking from the global queue to the individual registers.
You will end up with increased confusion from customers who always have to be on the lookout for next open spot at slightly higher waiting time and a more confusing store layout, all for just lower variance. Is it worth it?
Similarly, I’m not sure the global queue adds more than a step or two to routing, since you have to walk to the register either way, and it replaces a complex mental task, picking the optimal queue then monitoring if you should switch, with a simple one, waiting in a line while looking for a wave. In my experience, a global queue is less taxing than having to queue in lines would be.
It may or may not be worth the extra overhead.
In all single-queue systems I've seen, this is solved by the cashier pressing the "register free" button before being finished with the previous customers.
> You will end up with increased confusion from customers who always have to be on the lookout for next open spot
I find it, and I find it pretty clearly, for the opposite to be true. In single-queue system, I can literally sleep-walk and read books/browse social media the entire queue up until the point I reach the front end, where I only need to pay attention to the sign telling me to which register to go. With multiple queues, I feel the need to pay attention to whether or not another register is opening, or whether or not one of the customers in front of me has high handling time risk - so that I can switch queues early on.
That simply does not happen in the real world.
And this is why I always pick the global queue for self-checkout kiosks.
The only grocery store I knew that used it is the Whole foods on Harrison in SF. Technically they have 2 global lines/queues for some reason. (Pro-Tip the inside line is shorter because of the single turn in the line)
Perhaps it's something similar like with car vs airplane safety perception. Cars feel safe. Even though planes are extremely safe in reality, you are in control of your own car. Like you're at control in a self-checkout line.
That also makes me think about just how slow the self checkout systems are. The constant yelling out the price of the items I just scanned for confirmation just takes too long. I have to wait for it to stop to proceed. Also, how many times are the systems getting confused about whether you actually put the item in the bagging area or not requiring an attendant to be notified? UGH! </rant> The UI/UX people really need to fix this.
My local grocer has normal lanes with separate lines, express lanes with 6 checkers but a global queue, and the self checkout with a global queue. It seems like it is the family shoppers doing one huge weekly store trip in the normal lanes. Everyone else is looking to avoid them in the other two options.
Come to think of it, I mainly self checkout because I don't want to deal with another human.
I mean, the cashiers at the supermarket are very friendly and all, but... I just can't deal with small talk.
Oh you know, just most people? ;)