[philwelch]

It's another instance of "people are stupid". Yes, for any educated person it's obvious that one line is faster, that's the first thing about queueing theory, but most people don't know the first thing about queueing theory.

Other instances of "people are stupid" leading to poor design:

* Some cars come with a CVT (continuously variable transmission) rather than having to shift gears. The audible pitch of the engine just gradually goes up as the accelerator is depressed, rather than revving up and then shifting back down again. Since people were used to the gear-shifting behavior, they thought CVT's were underpowered, so they were actually redesigned to simulate the shifting behavior even though it was suboptimal.

* Coinstar machines are actually much, much faster than they appear. But people don't trust them if they don't take three times as long and make jangly coin sounds, so it just silently sorts the coins as fast as it can and plays a recording of jangly coin sounds, all the while delaying when it displays the final count onscreen.

[wisty]

A university lecturer of mine actually interviewed people in a bank, and asked them how long they thought they had stood in line. She found it was proportional to the line length, not the time they actually stood in line. Note, the bank didn't believe her, so she used some modelling package to animate it ... then they believed her.

[nandemo]

It's not at all obvious to me that one line is always faster (but then I only have a master's degree :-)). It might be faster in some situations, maybe slower in others.

In particular, the one-line system might significantly increase the average distance between (first-in-line) customer and nearest free cashier. Also, when there's a lot of cashiers, the customer might take more time to notice where is the nearest free cashier. I saw that happening the last time I checked-in for a flight.

In contrast, at immigration there is a long, single line but also short lines (1 to 2 persons) in front of each "cashier". These work as "caches" that minimize the delay I mentioned above.

[URSpider94]

As others have mentioned, one line feeding small cache lines is probably closer to reality, for the reasons that you mention -- buffering so that the cashier is always occupied.

The main goal is to prevent a single "price check" from jamming an entire line of people -- keep the queues at each station as small as possible so that most customers can route around the blockage.

[lywald]

It's obvious that one line is faster? Well it's not. Considering all cashiers are busy all the time, if it could be faster that would mean they have to manage multiple customers at the same time... If you're in the top 50% skilled at finding a line, then you're penalized because it just averages the queuing time.

[cynicalkane]

Most Nissans have a CVT now, and the ones I've driven seem to shift continuously. BMW tried implementing a discrete-shifting CVT like the one you describe for one of their semihybrids, and though I've never driven it, it got slammed in reviews. Do you have a citation for your claim?

[nik_0_0]

Do you have a source for that Coinstar playing jangly coin sounds?? I would love to read more about that.

[philwelch]

Well, this is embarrassing: I remembered that story from somewhere, and it turns out somewhere was another Hacker News thread: http://news.ycombinator.com/item?id=2007818

[JamesAn]

"Counting 600 coins per minute, Coinstar machines detect the metal content of the coin, as well as the size to accurately identify the coin denomination - and efficiently sort out all kinds of debris typically found in consumer coin. The company has found paper clips, key chains, wedding bands, gum wrappers, even teeth, all of which are identified quickly as non-coin."

http://web.archive.org/web/20100324183932/http://www.coinsta...