[reaperducer]

Meanwhile, 1 traditional checkout lane is open

I wish. The Wal-Mart near me no longer has staffed checkouts between 6am (opening time) and 8am. That's two hours in the morning of robots-only. I don't know about in the evenings.

traditional checkout lane is open with a long line.

I use the traditional check-out line whenever I can because where I live, the self-check line is almost always longer. It's not hard to keep an eye on the last person in the self-check line when you go to a real register to see which is faster.

I'm not a fireman on call. I'm OK spending an extra 45 seconds in a traditional line to keep a low-skilled human being employed.

[ryandrake]

I don't even think it's about going faster. In my experience, a traditional checkout staff is much faster than the self-check out. First of all, it's fantastically batched and pipelined. While the person in front of me is being checked out, I load all of my groceries onto the conveyer. Then, when it's my turn, the clerk does one motion over and over very quickly, and puts it on another conveyer that whisks it out of the way. When there's dedicated bagging staff, it's even more parallel.

Contrast that with self-checkout: There is no conveyer. You have to reach into your cart, grab one item, run it across the scanner, and place that item in a bag, then reach back over into the cart, grab one item, and so on. No pipelining at all.

I go the traditional staffed checkout route for the speed.

[jerlam]

This probably doesn't work for groceries, but Uniqlo (a clothing retailer) tags all their items with RFID. You put all your items in the "checkout box" at the same time and just pay, no scanning required.

Here's a video of it in use: https://www.youtube.com/watch?v=GqPfYnVKwGI