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Understanding the basics of queueing theory means that you will be eternally frustrated in most US grocery store checkout lines. And you may be kicked out for s

Understanding the basics of queueing theory means that you will be eternally frustrated in most US grocery store checkout lines. And you may be kicked out for screaming "Basically zero-cost queue synchronization and heavily variable server time means a global queue is better!"

vardump 8y ago
Why just US? I think that's pretty universal, at least in most western countries.
- scott_s 8y ago
  I don't have much firsthand knowledge of grocery stores outside the US, so I didn't want to over-generalize.
mikeryan 8y ago
This is getting better with self checkouts which tend to use a single Queue. 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)
- vardump 8y ago
  Those self checkouts are curious. Many people seem to take longer compared to traditional cashier line, but still prefer them. Maybe the same is true for me, although I feel I'm fast... 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.
  - badwolf 8y ago
    After working a checkout counter for a couple years as a teen, I cringe when I see how slow self-checkout makes you scan your items :(
    - Tor3 8y ago
      Not where I live - the scanner is as fast as it should be. One shop used to have two cashiers, now it has four self-checkouts and one cashier (I go there if I have some item that needs to be weighted and I haven't already done that by myself earlier. I also go there if the cashier has no customers and looks bored.. :-) It's definitely better and faster than before. My only gripe is that there's limited space for items, so it limits how much I can bring through there.
    - MrMember 8y ago
      Target overhauled their self checkout system a year or so ago and it's much better. You can scan items as fast as the cashier at a standard checkout would. When I'm at a different store that uses the old "please place item in the bagging area" system it's like stepping backwards in time.
  - dylan604 8y ago
    A decent checker usually has the codes for produce memorized, and are much faster than someone looking them up once a week or so. However, I have had some extremely bad checkers that I know I could self checkout faster than. Don't get me started on a bad sacker. 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.
    - TeMPOraL 8y ago
      Self-checkout situation is weird. Since there are no impulse-buying shelves in the checkout area, the store doesn't really benefit from people hanging around the machines. Which leads me to the conclusion that the piss-poor self-checkout UX, where you have to wait on the machine and can't really become a power user over time, must be either cluelessness of the manufacturers, or sabotage.
  - OnlyLys 8y ago
    > Many people seem to take longer compared to traditional cashier line, but still prefer them. 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.
- scott_s 8y ago
  Agreed. But I have experienced self-checkout setups that just replaced a normal station with a single self-checkout station, replicating the old behavior. These are being phased out near me.
defertoreptar 8y ago
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.
- roganartu 8y ago
  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.
  - munk-a 8y ago
    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.
    - defertoreptar 8y ago
      Flips to a page with a formula using sigma notation "This isn't rocket science bro. Obviously more lines = faster."
    - turtlecloud 8y ago
      If they could understand a book on Queuing theory they wouldn’t be working there in the first place.
      - 8y ago
zawerf 8y ago
If I remember correctly, in the mathematical model a global queue only helps with variance, but not the expected waiting time or throughput. 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?
- FakeComments 8y ago
  The Target by my house implemented global queuing at the registers and honestly, it’s the nicest store to shop at. 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.
  - scott_s 8y ago
    Yes, agreed, this is what I meant by “basically zero-cost queue synchronization”. Global queues tend to lead to more balanced systems, but at the cost of constant global queue access. But in grocery store checkouts, that cost is basically zero.
- SilasX 8y ago
  Yes, but variance is a thing you want to minimize too, since it forces entrants to be less efficient in allocating their own time since they have to block off more time to cover the n-standard deviations wait-time, which means they can’t be as efficient even if they get the fast queue since they didn’t schedule anything for that time. It may or may not be worth the extra overhead.
- TeMPOraL 8y ago
  > 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. 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.
keithnz 8y ago
who goes to a grocery store anymore? :) I just get mine delivered online. Though I have noticed that many stores( in New Zealand ) have global lines. Also with many grocery stores they have 3 independent ways of getting groceries, the classic find a Q you think is best to get a checkout person. Join a global Q for 12 items or less, or join a global Q for self checkout.
- anonytrary 8y ago
  > who goes to a grocery store anymore? Oh you know, just most people? ;)
- jacobsenscott 8y ago
  Online grocery shopping seems to be how stores ditch their lowest quality products. The produce is always on the verge of spoiling. You get the worst cut of meat, etc. And you pay extra for it. I never use it anymore.
  - TeMPOraL 8y ago
    I would think this doesn't matter for most of the things. Meat cuts maybe, but otherwise, the "best before" dates always seem tuned to maximize waste of perfectly good items, and with on-line shopping at least you won't end up participating in the silly game of "I won't buy anything that looks more than one sigma away from perfection".
- Tor3 8y ago
  Where I live it would cost a fortune to get grocery produce delivered to my home. Alternatively I could drive all the way to the post office.. which happens to be where there are lots of grocery stores anyway. And if I need milk or cream today, then there's not much help in ordering online.. it would take days. So I think I'll continue to limit my online shopping to electronic parts and the like.
  - billfruit 8y ago
    I thought it hardly took any extra charges to deliver to your address, atleast that's how it is in my country, only it might take about a day, since the home delivery grocers run a route and deliver to you as per their schedule though you can choose among the available slots.
kelp 8y ago
Many busy supermarkets in SF default to a single line. Trader Joe’s on Market, and Whole Foods on 4th do this. I’ve also seen it at Whole Foods in Manhattan, with reader boards to tell you which check out to go to. Works great!
- mertd 8y ago
  The reader boards work like a circular buffer. If you pay attention to where the pointer is, you may even jump ahead a few spots by entering the right queue.
  - TeMPOraL 8y ago
    Depends on the implementation. In Poland, in all the stores I've seen employing single queue for multiple registers, the board is controlled by cashiers - there's a button at the register that the cashier can press when they're ready for the next customer, and the board always displays the number of the register that signaled readiness most recently.
seanmcdirmid 8y ago
We are already getting the global queue with self checkout, though.
- scott_s 8y ago
  Well designed self checkouts. There are poorly designed self checkouts which replicate the same old structure. They are bad.
  - acidburnNSA 8y ago
    I experienced a new thing at the QFC at U Village in Seattle the other day. You grab a little handheld scanner on your way in, enter your customer number, and just scan stuff as you put it in your bag which is in your basket. Then you go to the self-checkout machine at the end, weigh the few things that need weighing, and pay. It's pretty fun!
    - seanmcdirmid 8y ago
      I haven’t tried this. From what I’ve seen, it doesn’t seem much faster than checking out the normal way. I don’t think it will be around much longer if usage at my local (downtown Bellevue) QFC is any indication.
    - grandmczeb 8y ago
      I’ve also seen this at the Wal-Mart in Mountain View - definitely a cool idea.
klenwell 8y ago
Larry David hears you: https://www.youtube.com/watch?v=M2CFFULmONk https://www.youtube.com/watch?v=M2CFFULmONk
jimmaswell 8y ago
It feels like a global queue might be unwieldy space-wise if a store's layout wasn't designed for it.
TimesOldRoman 8y ago
Costco is fantastic at everything...except the checkout process.
koboll 8y ago
>Basically zero-cost queue synchronization and heavily variable server time means a global queue is better! And this is why I always pick the global queue for self-checkout kiosks.
anonytrary 8y ago
I always hated that "oops I picked the wrong damn line" realization. At that point, it feels too late. It's way better if there's a single line and the cashiers shift the next person off the queue as soon as they are done handling their current person. Although, maybe psychologically it feels better for customers to have multiple lines to choose from?
colanderman 8y ago
I actually don't like global queueing for the simple reason that I have to keep moving. In a local queue, I can stop and ignore the world for a minute. 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.)

vardump 8y ago

Why just US? I think that's pretty universal, at least in most western countries.

scott_s 8y ago
I don't have much firsthand knowledge of grocery stores outside the US, so I didn't want to over-generalize.

mikeryan 8y ago

This is getting better with self checkouts which tend to use a single Queue. 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)

vardump 8y ago
Those self checkouts are curious. Many people seem to take longer compared to traditional cashier line, but still prefer them. Maybe the same is true for me, although I feel I'm fast... 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.
- badwolf 8y ago
  After working a checkout counter for a couple years as a teen, I cringe when I see how slow self-checkout makes you scan your items :(
  - Tor3 8y ago
    Not where I live - the scanner is as fast as it should be. One shop used to have two cashiers, now it has four self-checkouts and one cashier (I go there if I have some item that needs to be weighted and I haven't already done that by myself earlier. I also go there if the cashier has no customers and looks bored.. :-) It's definitely better and faster than before. My only gripe is that there's limited space for items, so it limits how much I can bring through there.
  - MrMember 8y ago
    Target overhauled their self checkout system a year or so ago and it's much better. You can scan items as fast as the cashier at a standard checkout would. When I'm at a different store that uses the old "please place item in the bagging area" system it's like stepping backwards in time.
- dylan604 8y ago
  A decent checker usually has the codes for produce memorized, and are much faster than someone looking them up once a week or so. However, I have had some extremely bad checkers that I know I could self checkout faster than. Don't get me started on a bad sacker. 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.
  - TeMPOraL 8y ago
    Self-checkout situation is weird. Since there are no impulse-buying shelves in the checkout area, the store doesn't really benefit from people hanging around the machines. Which leads me to the conclusion that the piss-poor self-checkout UX, where you have to wait on the machine and can't really become a power user over time, must be either cluelessness of the manufacturers, or sabotage.
- OnlyLys 8y ago
  > Many people seem to take longer compared to traditional cashier line, but still prefer them. 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.
scott_s 8y ago
Agreed. But I have experienced self-checkout setups that just replaced a normal station with a single self-checkout station, replicating the old behavior. These are being phased out near me.

defertoreptar 8y ago

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.

roganartu 8y ago
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.
- munk-a 8y ago
  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.
  - defertoreptar 8y ago
    Flips to a page with a formula using sigma notation "This isn't rocket science bro. Obviously more lines = faster."
  - turtlecloud 8y ago
    If they could understand a book on Queuing theory they wouldn’t be working there in the first place.
    - 8y ago

zawerf 8y ago

If I remember correctly, in the mathematical model a global queue only helps with variance, but not the expected waiting time or throughput. 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?

FakeComments 8y ago
The Target by my house implemented global queuing at the registers and honestly, it’s the nicest store to shop at. 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.
- scott_s 8y ago
  Yes, agreed, this is what I meant by “basically zero-cost queue synchronization”. Global queues tend to lead to more balanced systems, but at the cost of constant global queue access. But in grocery store checkouts, that cost is basically zero.
SilasX 8y ago
Yes, but variance is a thing you want to minimize too, since it forces entrants to be less efficient in allocating their own time since they have to block off more time to cover the n-standard deviations wait-time, which means they can’t be as efficient even if they get the fast queue since they didn’t schedule anything for that time. It may or may not be worth the extra overhead.
TeMPOraL 8y ago
> 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. 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.

keithnz 8y ago

who goes to a grocery store anymore? :) I just get mine delivered online. Though I have noticed that many stores( in New Zealand ) have global lines. Also with many grocery stores they have 3 independent ways of getting groceries, the classic find a Q you think is best to get a checkout person. Join a global Q for 12 items or less, or join a global Q for self checkout.

anonytrary 8y ago
> who goes to a grocery store anymore? Oh you know, just most people? ;)
jacobsenscott 8y ago
Online grocery shopping seems to be how stores ditch their lowest quality products. The produce is always on the verge of spoiling. You get the worst cut of meat, etc. And you pay extra for it. I never use it anymore.
- TeMPOraL 8y ago
  I would think this doesn't matter for most of the things. Meat cuts maybe, but otherwise, the "best before" dates always seem tuned to maximize waste of perfectly good items, and with on-line shopping at least you won't end up participating in the silly game of "I won't buy anything that looks more than one sigma away from perfection".
Tor3 8y ago
Where I live it would cost a fortune to get grocery produce delivered to my home. Alternatively I could drive all the way to the post office.. which happens to be where there are lots of grocery stores anyway. And if I need milk or cream today, then there's not much help in ordering online.. it would take days. So I think I'll continue to limit my online shopping to electronic parts and the like.
- billfruit 8y ago
  I thought it hardly took any extra charges to deliver to your address, atleast that's how it is in my country, only it might take about a day, since the home delivery grocers run a route and deliver to you as per their schedule though you can choose among the available slots.

kelp 8y ago

Many busy supermarkets in SF default to a single line. Trader Joe’s on Market, and Whole Foods on 4th do this. I’ve also seen it at Whole Foods in Manhattan, with reader boards to tell you which check out to go to. Works great!

mertd 8y ago
The reader boards work like a circular buffer. If you pay attention to where the pointer is, you may even jump ahead a few spots by entering the right queue.
- TeMPOraL 8y ago
  Depends on the implementation. In Poland, in all the stores I've seen employing single queue for multiple registers, the board is controlled by cashiers - there's a button at the register that the cashier can press when they're ready for the next customer, and the board always displays the number of the register that signaled readiness most recently.

seanmcdirmid 8y ago

We are already getting the global queue with self checkout, though.

scott_s 8y ago
Well designed self checkouts. There are poorly designed self checkouts which replicate the same old structure. They are bad.
- acidburnNSA 8y ago
  I experienced a new thing at the QFC at U Village in Seattle the other day. You grab a little handheld scanner on your way in, enter your customer number, and just scan stuff as you put it in your bag which is in your basket. Then you go to the self-checkout machine at the end, weigh the few things that need weighing, and pay. It's pretty fun!
  - seanmcdirmid 8y ago
    I haven’t tried this. From what I’ve seen, it doesn’t seem much faster than checking out the normal way. I don’t think it will be around much longer if usage at my local (downtown Bellevue) QFC is any indication.
  - grandmczeb 8y ago
    I’ve also seen this at the Wal-Mart in Mountain View - definitely a cool idea.

klenwell 8y ago

Larry David hears you: https://www.youtube.com/watch?v=M2CFFULmONk https://www.youtube.com/watch?v=M2CFFULmONk

jimmaswell 8y ago

It feels like a global queue might be unwieldy space-wise if a store's layout wasn't designed for it.

TimesOldRoman 8y ago

Costco is fantastic at everything...except the checkout process.

koboll 8y ago

>Basically zero-cost queue synchronization and heavily variable server time means a global queue is better! And this is why I always pick the global queue for self-checkout kiosks.

anonytrary 8y ago

I always hated that "oops I picked the wrong damn line" realization. At that point, it feels too late. It's way better if there's a single line and the cashiers shift the next person off the queue as soon as they are done handling their current person. Although, maybe psychologically it feels better for customers to have multiple lines to choose from?

colanderman 8y ago

I actually don't like global queueing for the simple reason that I have to keep moving. In a local queue, I can stop and ignore the world for a minute. 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.)