It always feels like whenever you are at the supermarket (or waiting on line at the DMV, or in traffic…or any line at all) that as soon as you switch to the line that is moving faster, it suddenly stops moving. There’s actually a reason for this.
Bill Hamack (Department of Chemical and Biomolecular Engineering at the University of Illinois – Urbana) explains why in the video that follows. After watching you will never look at the check out line the same. I now understand why the line at Whole Foods seems to be exempt from the rules of check out gridlock.
Turns out a study of phone systems in 1909 revealed the secret to a quick and smooth moving line. The basic idea was to figure out how many trunk lines (the circuit that connects the phones) you needed to run a phone system in a town.
A town could have one trunk line per telephone, but that would be costly and wasteful. The town’s second option would be to have enough trunk lines for the average number of daily calls, but this would cause stoppages during peak times).
In a supermarket, things work pretty much the same way: people arrive at the same time and if there are separate lines, this causes congestion at each particular line. So if a store only hires enough cashiers for the average number of shoppers per hour, then during peak times…you have congestion.
We still have not answered the question of why as soon as you change to that line that seems to move faster it seems to always stop. Here is why:
Multiple Single Cashier Line Scenario: In a regular single line scenario, a stoppage at one cashier means that none of those people are moving.
Single Line for Various Cashier Scenario: When there is one line for various cashiers, a stoppage at one cashier still keeps the line moving. If one cashier is stopped, the others are still getting people through and the crowd disperses. (Watch the video – it’s really cool).
Having one line for all the cashiers (at the average amount of shoppers per day) removes the stoppages. The problem for stores doing this is that psychologically, people want choice. Most shoppers feel empowered to when they have the choice of various lines. Whole foods has taken care of this in a great way. Take their store at Columbus Circle. There are various “single” lines that are manned by multiple cashiers. Shoppers still get to feel empowered with choice and the “single line various cashier” system keeps the flow moving. More retailers should take note.