You’ve taken a peek into nearly every line at the grocery store and selected the one that you think will get you checked out the fastest. Then you see someone in the next line over, who queued up two minutes after you, heading out the door well before all of your goods have even been bagged.

Photo credit: Shutterstock

Photo credit: Shutterstock

Feel like this happens to you every time you pick a line?

There’s probably a reason.

“When you’re selecting among several lines at the grocery store, the odds are not in your favor. Chances are, the other line really is faster,” Adam Mann for Wired wrote. “Mathematicians who study the behavior of lines are called queueing theorists, and they’ve got the numbers to prove this. Their models also underlie a diverse set of modern problems, including traffic engineering, factory design, and Internet infrastructure. At the same time, queueing theory provides a fairer way to checkout at the store. The only problem is that many customers don’t like it.”

Based on queuing theory, which Mann goes into detail about, there is no special trick to ensure you will always be in the fastest line possible.

“A grocery store tries to have enough employees at the checkout lines to get all their customers through with minimum delay. But sometimes, like on a Sunday afternoon, they get super busy. Because most grocery stores don’t have the physical space to add more checkout lines, their system becomes overwhelmed,” he wrote. “Some small interruption — a price check, a particularly talkative customer — will have downstream effects, holding up the entire line behind them.

“If there are three lines at the store, these delays will happen randomly at different registers,” Mann continued. “Think about the probability. The chances of your line being that fastest one are only one in three. Which means you have a two-thirds chance of not being in the fastest line. So it’s not just in your mind: Another line is probably moving faster than yours.”

To take care of at least part of this problem, queuing theorists suggest having all customers stand in a single long line and then each clerk serves the next person as they become available. This is similar to the method employed at several Trader Joe’s and T.J. Maxx stores, as well as many fast-food chains, for example.

“With a serpentine line, a long delay at one register won’t unfairly punish the people who lined up behind it. Instead, it will slow everyone down a little bit,” Mann wrote.

Unfortunately, Mann noted, many customers actually prefer to test their luck rather than stand in one long line.

Traffic lanes come with a host of other issues that can make one seem slower than the other. One of them, Tom Stafford for the BBC wrote, is the “universe-victim theory.”

“When my lane is moving along I’m focusing on where I’m going, ignoring the traffic I’m overtaking. When my lane is stuck I’m thinking about me and my hard luck, looking at the other lane. No wonder the association between me and being overtaken sticks in memory more,” he said, explaining the one of the psychological aspects that plays into lines.

Tom Vanderbilt, author of “Traffic: Why We Drive the Way We Do” who wrote of the “other lane” issue, among other observations of how traffic has shaped us, agreed with this psychological aspect in a Q&A.

“Given the general findings that humans are more sensitive to losses than gains, it doesn’t seem a stretch to imagine that this sense of being passed — of the other lane being faster — would stick out in our brains. All you have to do is pick out a benchmark car in the adjoining lane to see how often we fall for this illusion,” he said. “I’ve seen these cars pass well out of vision, only to find myself passing them again minutes later. Part of the reason this seesaw effect is happening in the first place is because of all the drivers ahead thought they could get a better deal, and basically ended up just shifting the equilibrium around temporarily.”

Front page image via Shutterstock.