Seoul and Braess’ Paradox
The Braess’ Paradox is, at first sight, very counter-intuitive. It reasons why a seeming improvement to a road network can actually worsen the traffic situation. There has been numerous cases, such as the construction of the Big Dig in Boston, where this phenomenon can be observed – a phenomenon in which the addition of a road to a congested road network increases the overall amount of time a driver spends travelling.
This paradox can also be applied to explain how removing a road improves traffic congestion. In 1968, an elevated road was built above the cheonggyecheon river in Seoul, South Korea in efforts to modernize the city. The road served to be useful until in 1980, when there was a massive increase in car usage as more and more people were able to afford cars. This sudden surge of cars caused the road to be permanently congested with cars. According to Braess’ Paradox, this congestion was caused because people knew that taking this road was the shortest path from their starting point to their desired destination. Because everyone acted to benefit themselves, nobody willingly took the other longer roads and this caused the congestion to worsen.
In 2005, the mayor of Seoul initiated a project to tear down the road and revitalize the cheonggyecheon river. It started mostly as a project to re-introduce nature to the city and to promote a more eco-friendly urban design. Kee Yeon Hwang, a professor of urban planning who was involved with this project since the beginning, said that he met with a lot of skepticism over whether removing the road would improve traffic conditions. Because of the counter-intuitive nature of the Braess’ Paradox, people didn’t believe it even after the research team worked on creating a road network model for months. According to Hwang, “The tearing down of the motorway has had both intended and unexpected effects. As soon as we destroyed the road, the cars just disappeared and drivers changed their habits. A lot of people just gave up their cars. Others found a different way of driving. In some cases, they kept using their cars but changed their routes.”
https://www.theguardian.com/environment/2006/nov/01/society.travelsenvironmentalimpact