Tearing town a highway to improve traffic in city
Highly populated cities like New York, Tokyo, and Seoul tends to have issue of traffic congestion throughout the city. Many commuters who commute with their cars get frustrated with how little official could do in order to improve this issue. For example, although adding a direct route from origin to destination seems to improve such traffic jams intuitively, this could either have no effect on the travel time or could even worsen people’s commute. This phenomenon that “adding resources to a transportation network can sometimes hurt performance at equilibrium” was first introduced by Dietrich Braess in 1968 and it has been recognized as Braess’s paradox. (Source: course textbook)
This phenomenon can be seen when Korean official decided to tear down one of the biggest highways in Cheonggyecheon, Seoul, called Cheonggye Overpass. Originally, the city of Seoul constructed a six-lane highway right above the Chun Yin River, aiming to improve the city traffic. However, this highway that connected major parts of Seoul was causing a severe traffic jams throughout the day. This is because the direct road changes the Nash equilibrium of the traffic flow between origin and destination, and since system tends to move toward the Nash equilibrium, it caused an over congestion in that road. This resulted in taking longer time to travel for the drivers compared to what it would have taken them if they took original side roads before Cheonggye Overpass was constructed. To people’s surprise, tearing down of Cheonggye Overpass improve the traffic flow.
When considering real life example like this, it is important to consider the selfish nature of humans. Even though the previous route will result in faster travel time, people do not have incentive to make agreement since selfish people will use the direct route to travel quickly just by themselves. Since other will follow them, trying to travel in less time as well, the traffic will naturally be concentrated on this one specific route.