Sep 10 2016
“[…] Choose a single line that leads to several cashiers
Not all lines are structured this way, but research has largely shown that this approach, known as a serpentine line, is the fastest. The person at the head of the line goes to the first available window in a system often seen at airports or banks. […]”
Sourced through the New York Times
Michel Baudin‘s comments:
No! Research shows no such thing. The serpentine line does not reduce the customers’ mean time through the system. Little’s Law tells us that, in steady state, regardless of how the queue is organized:
The mean service rate is the rate at which customers arrive into and leave the system. If there are 5 check stands each completing a transaction every 5 minutes on the average, the service rate is 1 customer/minute for the whole system. In steady state, there is also, on the average, one new customer arriving every minute.
The serpentine line still makes a difference, however, by reducing the variability of waiting times. With one line per check stand, you are occasionally stuck behind another customer taking exceptionally long. With a serpentine line, this is avoided. The slow customer will tie up one check stand for a long time, but the line automatically redirects the other customers to the other check stands.
Similar situations occur in manufacturing, with materials waiting in front of shared services like electroplating, painting or heat treatment. Manufacturers should get the math right, and so should the New York Times.