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To get across Hanoi, you have to go with the flow

What crossing the street in Vietnam's capital has in common with physics and thermal convection

By John Fox

“Don’t count on finding a traffic light,” the clerk cautions as we leave our hotel in Hanoi, jet-lagged and desperate for a meal. They’re few and far-between, especially in the tangled warren of centuries-old alleys and lanes that make up the city’s old quarter. “And don’t assume anyone will stop when the light turns red.”

Vietnam’s capital is a chaotic city of seven million people and five million motorbikes (the math adds up once you’ve seen a family of five piled onto a single scooter). Cars are too expensive for many residents, and public transportation is considered unreliable and inconvenient. The Vespa, therefore, reigns over the road, and chaos follows: Motorists go the wrong way on one-way streets, ignore lanes and cross-walks, and generally flout traffic rules. Their paths are so unpredictable that Hani Mahmassani, a traffic flow expert at Northwestern University, uses video clips of Hanoi’s traffic in his classes to highlight what he calls “the last frontier for autonomous vehicles to overcome.”

For a pedestrian, then, crossing the road in Hanoi is a learned skill, and not for the faint of heart. The hotel clerk has handed us printed instructions for “How to Cross Road,” wedged between spa hours and tips for haggling with street vendors:

Be relaxed and self-confident

Look two ways or keep your eyes on the drivers

Keep the speed slowly

Never look back

At first, my wife and I have a good laugh over what seems like excessive tourist-coddling. “Do they think we’re complete idiots or something?” But we’re grateful for the help as we stand on a street corner, hands clenched, about to leave the curb and step into an angry swarm of motorbikes.

At our first intersection, a churning confluence of rubber and metal, we pause and survey the scene. New arrivals to the city cower anxiously on corners, while locals and battle-tested tourists hardly break stride as they slide into the current. My wife deftly moves to my downstream side. Though it’s disconcerting to have your spouse of 20-plus years use you as a human shield, her logic seems at least defensible: I’m nearly a foot taller than her, so more visible. And my gray hair might elicit more respect, so motorists give us a wider berth.

“New arrivals to the city cower anxiously on corners, while locals and battle-tested tourists hardly break stride as they slide into the current.”

Following the instructions, we look both ways, only to confirm that — yes — there is an unbroken stream of traffic moving toward us. We draw deep breaths and make our move, leaving every shred of instinct and agency at the curb as we give over to the elements. We walk at a steady, predictable pace as scooters and the occasional car swerve and dance around us. It’s like we’re in a life-sized game of Super Mario Brothers where Hanoi is the Mushroom Kingdom, and the hazards magically avoid us rather than the other way around.

Photo by Maika Elan/Bloomberg via Getty Images

But how exactly does this game operate without any hand on a controller? What seems on the surface a recipe for disaster somehow mostly works. When I return home, I ask a physicist friend if there’s some universal law that might explain it. He notes that Hanoi traffic has loose parallels with Bernoulli’s Principle, where traffic is the fluid and we pedestrians are the curved objects it flows around.

But, of course, there are humans on those motorbikes. Some are distracted, others are having a bad day, and each is making split-second decisions and turns based on limited information. So there’s clearly more than physics at work.

That’s where Mahmassani’s studies come in. The engineering professor describes Hanoi as a classic case of a “seemingly chaotic traffic environment where amazing self-organization somehow prevails — and eventually fails, sometimes spectacularly.” Self-organization is a natural principle, first recognized in ancient Greece, that has been used over the centuries to explain everything from thermal convection to animal swarming to market economics. It describes situations in the natural and social worlds where order forms spontaneously — and often inexplicably — from the elements or participants in an otherwise disorderly system. This may be as close as I’m likely to get to an explanation for how my wife and I make it to the banh mi shop and back in one piece.

After a week in Hanoi I become a seasoned pro, expanding my repertoire from narrow lanes to dauntingly wide boulevards. I come to love the city and the freeing sense of being swept up in its imperfection. And should I ever find the guts to contemplate sky diving or bungee jumping — or plunging into any other void of uncertainty — I realize I have my instructions: Be relaxed. Never look back.

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John Fox is a writer based in Boston.

Top photo by Ye Aung Thu AFP/Getty Images


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