A single line to 3 cashiers is ~3x faster than a separate line for each cashier • Hacker News Board

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#81

Post by philwelch » Thu, Dec 08, 2011, 6:46 PM UTC

ck2 wrote: post #65

It's not a matter of logic. When there is one cashier and a dozen customers waiting, that tells me the store is too cheap or too mismanaged to have other cashiers scheduled. The best thing a store can do for customer relations is to open additional registers when too many customers are waiting, it implies the customer's time is important. I also enjoy discovering it was the store manager themselves running the extra…

Yes, but that's not the point. How do you allocate the extra cashiers? Do they just take customers one by one from the existing queue, or do they split the queue awkwardly and encourage customers to form additional queues?

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#82

Post by scott_s » Thu, Dec 08, 2011, 6:49 PM UTC

pnathan wrote: post #27

FYI: This is an example of the branch of mathematics called queueing theory. http://en.wikipedia.org/wiki/Queueing_theory It's a fascinating study requiring a good knowledge of probability to use beyond the simplified models. It turns out from the math that throughput using a single queue is better than using multiple queues.

The problem with learning even basic queuing theory is that, for the rest of your life, you will think "There is a much better way to do this, and I can prove it" after having to choose a single line.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#83

Post by finnw » Thu, Dec 08, 2011, 6:50 PM UTC

tomkarlo wrote: post #67

Splines wrote: post #62

A blend is probably a better choice. It's obvious that single queues for each cashier isn't very efficient, but the tradeoff is that lines are visibly shorter, and progress to the goal is clear. Having a single line for all cashiers (ala Fry's Electronics or an airline ticket agent) is more efficient, but the long line, logistics of finding the next available cashier, and uncertainty of completion make for a frustrat…

Having more than one line materially increases stress for shoppers, because the choice implies they might be on the "wrong" line. So they worry more about how fast they're moving, etc. If you only have one line, you can tell people exactly how long the wait is (because the average transaction time is very stable) and customers don't have to worry about making the right choice.

Having one combined line can increase stress for shoppers too, especially if the line isn't clearly marked by barriers.

What happens is, another customer comes along, sees three cashiers and one queue (in the middle) and decides to join the "empty queue" in front of the cashier at either end.

Of course they know there's only one queue and that they are queue jumping, but they calculate that they can pretend they didn't know.

I assume there's a cultural factor here. I'm in the UK and have seen this many times in one store nearby, but I imagine that in some parts of the world you would be beaten or shot for it. I have never seen anybody complain about it, they just temporarily disperse into three queues (which is awkward because there is not really enough room.)

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#84

Post by mahyarm » Thu, Dec 08, 2011, 6:50 PM UTC

rdtsc wrote: post #43

pnathan wrote: post #27

FYI: This is an example of the branch of mathematics called queueing theory. http://en.wikipedia.org/wiki/Queueing_theory It's a fascinating study requiring a good knowledge of probability to use beyond the simplified models. It turns out from the math that throughput using a single queue is better than using multiple queues.

Not trying to be condescending but doesn't it surprise anyone here that this is _not_ obvious? At least on this site, there are still people doubting or debating this. So I am wondering why don't stores do this already. And I believe it is because of perceptions. They understand that time will be saved, however, they realize that most people will be scared by a long line. One long line that moves fast will still appe…

At a walmart in Canada, they had an express line which had 6 cashiers and one line. A LCD screen chimed with the number of the next cashier when they were ready.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#85

Post by eiji » Thu, Dec 08, 2011, 6:52 PM UTC

smackfu wrote: post #18

nlawalker wrote: post #9

Most of the grocery stores in my area have installed self-checkout systems that are especially great if you just have a handful of items that all have UPCs (no produce or bagged bulk), don't have any items requiring an age check and possess at least the intelligence of a fifth grader. I mention this not just because it's relevant to the idea of waiting in line at a store, but because in every store where I've seen th…

Around here, the grocery self-checkout works the same as the normal checkouts, mainly because they just replaced the normal ones in place. (Also, self-checkouts suck. I bet their throughput is terrible compared to manned checkout lines. That teenage checkout girl is WAY better than I am at scanning stuff.)

Self-checkouts are not just about speed. They also appeal to specific kind of people.

I use them because I don't want to interact with someone just to get some groceries. I know, it's kind of sad, but I don't want to say 'Hi' and 'Thank you' and I don't want 5 bags when 2 would suffice and don't want to explain that, so I just do it myself.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#86

Post by AndyNemmity » Thu, Dec 08, 2011, 6:53 PM UTC

cheald wrote: post #74

rdtsc wrote: post #43

Earlier quoted context omitted.

Not trying to be condescending but doesn't it surprise anyone here that this is _not_ obvious? At least on this site, there are still people doubting or debating this. So I am wondering why don't stores do this already. And I believe it is because of perceptions. They understand that time will be saved, however, they realize that most people will be scared by a long line. One long line that moves fast will still appe…

Fry's Electronics does the single line thing, and any time there is a line, I feel like I end up standing in it longer than I would at a grocery story. I suspect this is probably psychological, but letting me, as the shopper, pick the line I want to stand in puts me in charge of how long I wait. If I pick a bad line, it's my fault for picking the bad line. When there's just one line available, I don't get that choice…

I go to Fry's a ton, and it always seems to go much quicker, but I agree, psychologically standing in a tremendously huge line feels worse.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#87

Post by j_baker » Thu, Dec 08, 2011, 6:54 PM UTC

Another change: As soon as there are three or more people waiting in a line, the retailer deploys "line busters," employees who scan items in shoppers' carts before they reach the cashier, says Mr. Carey, who works closely with the retailer's operations team on line speed.

This isn't really news. WalMart's been doing this forever.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#88

Post by j_baker » Thu, Dec 08, 2011, 6:56 PM UTC

smackfu wrote: post #28

What I didn't see in this article is why retailers don't do this today. I see a lot of positives listed and no negatives, so it seems like a no-brainer, right? Yet the biggest retailers like Walmart and Target have tons of lanes, and even do staggered front/back lanes which are terrible for the customers. Is it because there are negative feelings to seeing a long line, and that people do not expect it to be fast so t…

Actually, the article did mention one strike against using one line (albeit briefly):

And they prefer to choose their own line rather than wait in a single-file line for the next available register—even though that set-up has proven to be faster, research on queuing shows.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#89

Post by j_baker » Thu, Dec 08, 2011, 6:59 PM UTC

getsat wrote: post #32

smackfu wrote: post #28

What I didn't see in this article is why retailers don't do this today. I see a lot of positives listed and no negatives, so it seems like a no-brainer, right? Yet the biggest retailers like Walmart and Target have tons of lanes, and even do staggered front/back lanes which are terrible for the customers. Is it because there are negative feelings to seeing a long line, and that people do not expect it to be fast so t…

Illusion of choice.

Well no. There's no illusion to it. Customers do get a choice. Of course, the important question is how much that choice gets them.

Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier

#90

Post by MaysonL » Thu, Dec 08, 2011, 7:05 PM UTC

dxbydt wrote: post #79

scala> import org.apache.commons.math.distribution.{ExponentialDistributionImpl=>expo} //pc = process customer, with a mean time mu per customer scala> def pc(mu:Int):Double= new expo(mu).sample // q = queue of n customers with mean process time mu scala> def q(n:Int,mu:Int):Double=(1 to n).map(_=>pc(mu)).sum scala> // put 3000 people in 1 queue with mean process time 50 scala> (1 to 1000).map(_=>q(3000,50)).sum/1000…

But of course this is BS, because the three queues are not independent. Try it with 1 queue which feeds into whichever of the three queues is currently shortest. And of course, in grocery stores, where one can unload one's cart while the person ahead is being processed, there's an advantage to multiple lines.