[Bostwick]

One queue adds an overhead for the time it takes for the person at the front of the queue to notice a cashier is free and walk to that cashier. I have watched this system in action at the Post Office, Rail stations, and one supermarket and this overhead can be significant. One supermarket actually employs somebody at the head of the queue just to tell them which cashier to go to and when.

Whole Foods in NYC has solved this problem by having one queue, but when you get towards the front, there are five separate, color-coded lines. At the front of the queue is a giant television that shows a bar of color for each lane. When a register opens up, the number for that register slides into the color bar for the next person in the sequence, and a voice announces "Register 12". It's fairly efficient at keeping the queue moving as well as managing people's psychological need for multiple lines. It also prevents cashiers from wasting time, because as soon as a transaction is finished, their register is automatically assigned to the next person in the queue. The only "wasted" time is the time walking from queue to register, and pleasantries.