November 14, 2011 1 Comment
I have seen several styles of queueing in practice recently.
Trader Joe’s in dc has a long snaking line feeding a whole bunch of register in a strictly FIFO manner. An employee stands between the registers and directs customers to the next open register.
Safeway has a traditional grocery store model, where there are lots of independent queues, with a few express lines as well.
CVS has almost entirely switched over to a small number of self-checkout kiosks. There is no real concept of queueing- people gather in a bunch and self-organize who’s next. This reminds me of “lines” that I saw in Israel.
Costco has a bunch of independent queues, but has no express lanes (besides, who goes to Costco for fewer than 10 items anyway?)
So these are over the place – it should be obvious that FIFO will on be the best strategy (i.e. have the shortest average wait time) while Safeway offers the highest throughput priority queue (which it achieves by reducing the number of queues available to non-priority customers, and thereby both increasing the average wait and increasing the speed differential between the priority and regular queues).
The CVS approach is a random lottery: there’s no way to predict all of the possible situations, and the efficiency loss is a greater than linear function of the number of people present (think CSMA/CD in a half-duplex environment).
And of course the Costco approach is the most familiar: its average wait will be a little bit better than Safeway, but the range of wait times will be larger than that of the non-priority queue at Safeway.
And now I’ve seen something new: the new Whole Foods in Foggy Bottom has a queueing strategy I’ve never seen in a store before. There are a variable number of lanes which are drained in a not-quite round-robin fashion, and they are drained to a common pool of tellers. The draining process causes a fair amount of confusion as people are sent to registers variable distances from the queueing line. The confusion increases when multiple lanes are drained at the same time.
My gut reaction to it is that it’s needlessly complex- it’s esoteric for it’s own sake, like much modern art and architecture. I prefer simple to complex as a general rule, which is part of why I am skeptical of technocratic social engineering and the like. Gears and other simple machines let you move power from one place to another, but even the best machines lose work to friction.
Anyway, given that the WF approach does not differentiate between the lanes, I’ve had a hard time understanding why they wouldn’t be better off with a strict FIFO line. I still don’t understand it, but my theory is that the WF designers thought that the psychological problem of equal queues (I always get the slow line) was better than the psychological effect of the snaking FIFO line. I’ve heard a tremendous number of people complain about the length of the TJ’s line, even though they’ll get through it faster than any other type, so perhaps WF has a point.
As for me, I’d take FIFO any day- it’s a truly fair approach to queueing, and is a maximally efficient use of resources, and that appeals to my conservationist (née hippy) side.