Why you always seem to choose the wrong line

Bad choice.
Bad choice.
Image: Reuters/Brian Snyder
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Today is midterm election day in the US, meaning millions of Americans will be standing in line at any given moment. Fortunately, because they’ll have little to no choice about where to wait, they will be spared one of the agonies of this custom: trying to gauge which line is moving fastest.

If you’ve shopped at an old-school grocery store with a single row of cashier lanes, entered the US at a busy border crossing on land, or had to select a security line at an airport, however, you’ve experienced this angst. We’ve all devised our own formulas for selecting a winner—avoiding the chattiest cashier, for instance, or the obviously flummoxed first-time travelers.

Here’s the bad news. Though a handful of tactics may work in specific cases, your strategies are probably for naught. According to mathematicians who study queuing theory, there is no secret to selecting the shortest lane.

Journalist Adam Mann has explained why in Wired, writing:

“Because most grocery stores don’t have the physical space to add more checkout lines, their system becomes overwhelmed. 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. 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.

The astute, time-conscious reader will note that newer supermarkets, including Trader Joe’s in the US, rely on a system that’s logically superior. Customers join one “serpentine” line and are directed to the next available cashier when they’ve reached the front. Queuing theorists say this system is about three times faster for everyone.

Meanwhile, Whole Foods combines the multi-queue and single-line philosophies in a hybrid approach that allows you to pick the shortest serpentine line, which may be smartest answer, considering human psychology.

Unless they’re moving swiftly, serpentine lines look like long, miserable death marches. At the Trader Joe’s near the Quartz office in New York, the line can snake around the outside aisles and stretch back to the front doors. Forget it, one thinks, spinning on one’s sneakers and exiting through the entrance.

We’re not rational people, and as Mann notes, we like to believe we can shrewdly beat the system. Give us multiple lines, and we see an opportunity to prove our capacity for self-reliance. That spirit may be crushed, however, by the indifferent whims of chance.