Congestion and Complexity
How a system defeated common sense.
2 min read · from UNINTENDED by Mayank Mehta
For as long as cities have had traffic, the solution to congestion has seemed obvious. Build more roads. If one highway is jammed, add another lane. If a bottleneck forms, create a bypass. More capacity equals less congestion. It's so intuitive that it barely qualifies as an idea. It's just common sense.
Except it's wrong.
In the center of Seoul, South Korea, there once stood a six-lane elevated expressway called the Cheonggyecheon. It carried nearly 160,000 vehicles a day and was, by every standard metric, a major artery of the city. It had been built for exactly the reason you would expect: to relieve traffic. And like so many roads built for that purpose, it had failed to do so. Traffic was still slow. Pollution had worsened. The neighborhoods beneath the expressway had decayed into shadow.
In 2003, the city did something that violated decades of traffic engineering orthodoxy. It tore the highway down.
Not redirected. Not redesigned. Demolished. A six-lane expressway carrying 160,000 cars a day was removed from the map.
According to every model, traffic should have become dramatically worse. A major route had vanished. Capacity had been reduced. There was nowhere else for all those cars to go.
But traffic didn't get worse. It got better.
Once the expressway was gone, traffic patterns reorganized themselves. Some trips that drivers used to make simply disappeared. Others were rerouted. Commuters who had been drawn to the expressway because it looked like the fastest option stopped converging on that corridor, because the option no longer existed. The system found a new equilibrium, one with fewer vehicles in the city center and higher average speeds on the remaining roads.
Nothing about human nature had changed. Nobody suddenly became more patient or more civic-minded. The improvement came entirely from the structure of the network. The missing road had been a trap. By offering an apparently optimal shortcut, it pulled traffic into patterns that slowed everyone down. Removing it simplified the network and eliminated the distortion.
This phenomenon has a name in mathematics. It's called Braess's paradox, after the German mathematician who proved that adding a new route to a network can, under certain conditions, make overall performance worse. The extra option doesn't help the system. It misleads it.
Seoul's lesson was a cold one. The city didn't get better because people got smarter. It got better because the network stopped lying to them. Sometimes congestion isn't a shortage of roads. It's an excess of choices.