
Queueing Theory — Why the other lines always seem to move faster than yours - hugoahlberg
http://flowingdata.com/2010/12/24/why-the-other-lines-always-seem-to-move-faster-than-yours/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+Tputh+%28TPUTH+-+Breaking+News+With+The+Social+Hammer%29&utm_content=Twitter
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bhc3
I remember discussing this in operations class. If I recall correctly, the
biggest issue with the single line approach is one of perception. Customers
see a really, really long line and decide to skip shopping at a location.
Despite the fact that this is more efficient allocation mode of checkout
"supply" for the checkout "demand".

I believe Disney may have put some effort in masking the length of the single
line to address this issue. Might be something that grocers could learn.

A couple factors, though, would seem to undermine grocers' incentives to
change their queuing approach:

One is the need to maximize inventory on the sales floor. They would need to
do a lot of reconfiguration to handle the single line. And that might
potentially reduce floor space for stock.

The other issue is that grocery stores fill a core human need: food. We're
going there regardless of the line configuration.

I'll bet some grocer out there could make a name for themselves by shaking up
the traditional ways we shop. This queuing idea is one example. Would be a
smart move in fairly commoditized industry..

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jganetsk
Trader Joe's has a single queue with multiple registers.

They do plenty of other "shaking up traditional ways we shop", or at least
their marketing folks would have you believe.

~~~
jamesbritt
"Trader Joe's has a single queue with multiple registers."

Wish they did that in Phoenix/Scottsdale.

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sorbits
tl;dr; Out of 3 lines, yours will be the fastest only ⅓ of the time.

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Amnon
It will also be the slowest only 1/3 of the time, so in fact this isn't an
explanation why "the other lines" seem to be faster.

~~~
bryanh
I think the effect is the result of fixating on the fact that there was a
faster line, not that there are slower lines.

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zitterbewegung
Interesting, Fry's electronics does exactly this. They have one line which
feeds into n registers.

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maw
In Walmarts in Mexico there are many 20 items or fewer registers; these are
all fed by a single line. At busy stores during busy times these single lines
can extend well over 100m. People complain about the long lines, but they do
move quickly -- well, as quickly as anything moves here.

~~~
jamesbritt
I've wondered about the effectiveness of these "express" lanes.

What's the biggest time sink? Ringing up items? Payment processing? Bagging?

I think it's payment, unless there are a lot of items, and/or the casiher is
the one doing the bagging as well.

Many cashiers can pull through dozens of items pretty quickly, faster than it
takes for the customer to dig up the right card or find the checkbook, and
then some ID, etc.

It may be best to just pick the line with the fewest customers regardless of
whether any line is supposedly express, unless the cashier is also the one
doing the bagging.

~~~
maw
I've wondered as well.

I worked as a cashier in a grocery store when I was in high school. At our
store we had two "main" express lines, one for twelve items or fewer, one for
eight. Except for very quiet times, when there was only one cashier on duty,
the twelve item line was open and the eight item line wasn't. (Any of the
other lines could also be turned into express lines by setting a switch at the
register, but they were less clearly marked, so lots of customers didn't
notice them. They were only rarely activated.)

Your intuitions square with mine: payment was usually the biggest time sink,
especially with checks and cards. Still, there were plenty of sources of
variation: some items were hard to scan quickly, some customers had more
produce that needed to be weighed, sometimes an item wasn't in the database or
there was a dispute about its price and it needed to be checked, some lines
had baggers--excuse me, service clerks--and some didn't.

And, of course, some cashiers were just faster than others. Interestingly,
there was no clear pattern here. Experience (having produce codes memorized,
knowing how to scan tricky items or even having their UPC codes memorized, and
being good at counting cash quickly and accurately) played a role. Mostly,
however, people seemed to be intrinsically motivated to do their work well, or
else they weren't. We high school kids weren't collectively faster or slower
than the "old people."

Some customers were faster than others too: cash payment was definitely faster
than card, and both were much faster than check. (This was 15 odd years ago;
card is likely faster than it used to be, but likely still slower than cash.)
Some customers insisted on paying with exact change, and many of them would
take their sweet time doing so. Also, some customers would come with lots of
coupons, which would take time to scan.

My hunch at the time was that we'd have gotten better throughput by keeping
the eight item line open, cash-only, no coupons. I think I was probably right,
given the constraints: we were going to have an express line, regardless of
whether it was really more efficient or not. Might as well optimize it.

Now, I think that several feeder lines would be more efficient. Maybe just two
(express and regular), maybe three or four (although I distrust people's
honesty as well as their ability to count).

<http://blog.mrmeyer.com/?p=4646> has shown up on HN at least twice, and it's
worth reading.

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albemuth
That time were there was an onslaught of erlang articles on HN there was one
called something like "Erlang the movie", for some reason Erlang telephony
videos make me happy :)

