An estimated 7.5 million Americans traveled by plane during the winter holidays this past year. Some passengers may have rushed to check in, get through security and find their gate—only to get stuck in a slow-moving slog to board the plane.
Scientifically speaking, there are more efficient ways to get customers to their seat. These methods could help reduce the amount of time and stress that people experience at the airport—and save airlines a boatload (or a planeload) of money. But these more efficient methods, developed using computer models, might come at too high a cost for both airlines and their passengers.
Scientists have been searching for ways to streamline the boarding process for decades. In 2005 Jason Steffen, an astrophysicist at the University of Nevada, Las Vegas, became captivated by the problem after getting stuck in a long line at the jet bridge at Seattle’s international airport. So he turned to his computer modeling skills, which he usually reserved for studying the movement of exoplanets, to find a better way to board.
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Initially, like many travelers, Steffen assumed that boarding a plane back to front would be easiest, because the first people to board could walk straight to the back, preventing a bottleneck in the aisle. Many airlines, including Delta and United Airlines, have at one point used some variation of this method.
But Steffen’s simulations proved his gut instinct wrong: this seemingly superior solution turned out to be one of the worst. The simulated passengers still got bogged down as each row tried to store their overhead luggage at once, blocking the aisles. Overall, this approach took the same amount of time as the “worst possible scenario”: boarding front to back.
“That’s when I was like, ‘Okay, so this problem is actually more interesting than I thought,’” Steffen says. He used a specialized algorithm to randomly change the virtual passengers’ boarding order. After each change, he ran the simulation to check whether it improved boarding time. After hundreds of iterations, he found that the most efficient boarding method was a version of back to front—with a few key twists. Rather than have passengers fill in each row sequentially, it was best to start boarding from the window seats, skipping every other row along the way. Effectively, this means that people with an even-numbered window seat would board first, followed by those with an odd-numbered window seat, those with an even-numbered middle seat, and so on. According to simulations, this approach was twice as fast as the front-to-back boarding strategy and 30 percent faster than random boarding.
In the 16 years since Steffen’s results were published, this approach has become known as the Steffen boarding method. It works because the leapfrogging strikes the optimal balance between having passengers in the aisle versus in their seat at any given time. It also spaces customers out enough to avoid causing a traffic jam—at least, in a perfect world.
“Steffen has the best of all available models as a boarding model,” says Hassan Zeineddine, a supply chain researcher at American University in Dubai. “But it’s way far from [being] practical.”
Unfortunately, real people don’t behave in mathematically ideal ways. “A large percentage of passengers do not follow the instructions given at the terminal,” says Tomasz Kisiel, a transportation engineer at Wrocław University of Science and Technology in Poland. “This is not surprising,” he says, but does throw a wrench in Steffen’s technique.
To board in such a precise order, people would need to either receive a random seat assignment based on their spot in line or board in a specific predetermined order—both of which have significant drawbacks. If people were expected to board in a predetermined order, they could easily miss their number being called because they arrived late to the gate or weren’t paying attention. People assigned a random seat number based on their spot in line might be confused or dissatisfied with their assigned seat. And Steffen’s method allows groups of people to either board together or sit together but not both—a huge drawback for families traveling with small children and groups such as students traveling with a teacher chaperone.
So Zeineddine, whose work focuses on transportation and supply chain logistics, set out to make Steffen’s method more practical. His upgraded technique, which he dubbed “dynamically optimized boarding,” involves two major changes: First, passengers traveling together board as small groups called “cliques.” And second, an algorithm automatically sorts and queues travelers upon check-in. Individual passengers and small boarding groups can then be called to the jet bridge using a phone notification. Though about 5 percent less efficient than Steffen’s boarding strategy, this method comes close to achieving optimal boarding time while also accounting for the human element, Zeineddine says.
Every minute spent parked at the jet bridge costs airlines money, so shaving off boarding time could add up to real savings. So why don’t airlines give these techniques a shot? “When it comes to implementation, there is always resistance,” Zeineddine says. Such a thorough revamping of the boarding process across every airport would require a massive logistical lift. “It’s basically ‘if it isn’t broken, don’t fix it,’” he says.
Airlines also have to think about customer experience. While many people aren’t fans of current boarding strategies, they might dislike a riff on Steffen’s method even more. Plus, switching to speedier boarding could affect an airline’s ability to offer additional paid options such as first class, business class and priority seating.
Some airlines already use more efficient—though not fully optimal—boarding methods. United Airlines recently began using the windows-middle-aisle approach (nicknamed WILMA), which bears some resemblance to Steffen’s method by boarding window seat passengers first. Other airlines use more “random” approaches, which studies have shown to be faster than block boarding strategies such as back to front or even WILMA. For example, Southwest Airlines uses a buslike approach in which people are assigned a place in line in a boarding group and choose their own seat as they walk down the aisle. Other airlines, such as the Ireland-based Ryanair, use a first come, first serve seating method for passengers who pay extra, while standard seats are assigned randomly.
Whether or not his method ever becomes the new boarding standard, Steffen is happy to have shaken up how people think about the logistics of flying. For the foreseeable future, though, the ordeal remains an exercise in hurry up and wait.