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Braess’ Paradox – The Cheonggyecheon Restoration Project

Last week, we learnt about different aspects of Game Theory, and one of them involved flow through network paths. This could be applied to traffic flows through roads, and we learnt about an interesting, and seemingly unintuitive paradox known as the Braess’ Paradox that stated that adding resources makes everyone worse off. In other words, adding a road may increase travel time instead of decreasing it.


A real life example that elucidates this paradox and caught my attention was the Cheonggyecheon Restoration Project in Seoul, South Korea, in which a typically traffic-choked elevated highway was taken down and turned into a waterway, and public recreation area to make the city more eco-friendly and sustainable. The change in the face of the region is shown in the pictures given below.



Rapid population growth, urban development, economic growth and automobile consumption caused Seoul to have a major traffic problem. The Cheonggyecheon highway was a major carrier of the city’s traffic. Therefore, there was a lot of fear regarding the replacement of this crucial road with a public waterway, since it was thought that this would exacerbate the traffic problem in the city.

However, to everyone’s surprise, traffic flow actually sped up around the region, with travel times reducing. This can be explained using Braess’ Paradox. This is based on driver motives. In the presence of the highway (with ‘optimum’ drive time), all drivers would prefer to use the road, thus congesting it. However, in its absence, this traffic would get scattered across several other roads, which would reduce total travel time.

A more mathematical explanation of this is given below. This situation can be modeled as follows. Suppose t = 400 cars want to travel from points A to D. If they use the Cheonggyecheon highway, then the total time taken by them will be 80 minutes. However, if there is no highway, and half the cars go from ABD, and the other half go from ACD, then each car takes 65 minutes, which is a better travel time for each car.


However, we cannot attribute all the success to just the Braess’ Paradox. Factors such as the government’s increased investments in public transit systems would also have played a part in this. More so, human decisions wouldn’t always be the same as expected, and that is the beauty of this being a social science. For example, on a particular day, more drivers may just happen to choose one route over the other, changing optimum travel routes and times. However, the general overview and concensus is that the Braess’ paradox had a major part to play in the lessening of traffic in Seoul, and multiple restoration projects around the world are following its lead.



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September 2017