The Braess Paradox is Alive and Well in the Streets of New York City
The Braess paradox states that adding a new strategy to a game can make everyone worse off. From this paradox, we discern that building new roads can increase congestion and removing existing roads can decrease traffic. The logic behind the paradox is similar to the Tragedy of the Commons – individuals act in their best interest instead of cooperating to achieve the best possible outcome for everyone. Thus, drivers will always choose the route that has the shortest travel time, regardless of how it affects everyone else. Traffic congestion and commute times are a prevalent issue in New York City, where relatively short commutes can take ages. The implications of Braess paradox can be highlighted in historical and current examples of traffic congestion in NYC.
In 1990, the New York Times published an article that hypothesized what would happen if the closed 42nd street – a main street through the center of Manhattan. On Earth Day of that year, the city’s Transportation Commissioner actually shut down 42nd street. Many thought that this action would result in unbearable traffic jams, constant honking, and frustrated drivers. However, quite the opposite occurred – there was no historic traffic jam and congestion was actually alleviated from this closure, an early demonstration of the Braess principle in action in New York City.
Later, the city utilized this theory to reduce traffic on a much larger scale. In 2009, Transportation Commissioner announced that he would shut down Broadway between 42nd and 47th streets. Officials hypothesized that closing this block would reduce traffic congestion because the diagonal nature of the street causes inefficiencies where it intersects with other streets. In 2010, the city actually implemented this change to the traffic pattern which decreased traffic times along Broadway by 15%.
We can demonstrate this using the diagrams below. In this example, 1,000 commuters are trying to get from point A to point B using different streets in midtown Manhattan that have different travel times. For the purpose of this example, the time necessary to get across Broadway is 0 minutes. The equilibrium commute time with Broadway is 20 minutes. All 1,000 drives are going to take AB over AC because 1,000/100 is 10 which is less than 12. In a similar sense, all drivers will choose CD over BD for the exact same reason. In the second graph, we remove Broadway and instead block it off for pedestrians and bikers. In this new system, the 1,000 drivers divide themselves evenly among the two routes and the equilibrium commute time is 17 minutes, 3 minutes less than the original commute.
Not only was congestion alleviated, it reduced pedestrian injuries in the area by 35% and driver/passenger injuries by 63%. Foot traffic increased and a majority of businesses in the affected areas requested the traffic structure become permanent, and it still is over a decade later.
NYC has continued to experiment with its traffic patterns today. When the Covid-19 pandemic began in NYC, the city created “Open Streets”, a program that blocked off streets to cars in order to provide space for pedestrians to walk while remaining socially distanced. Some of these open streets are reverting back to streets for cars. It will be interesting to see how adding these streets back to the traffic network will impact congestion in terms of the Braess paradox. Overall, the Braess paradox has and will continue to define traffic patterns in New York.
Sources
https://www.nytimes.com/2022/08/11/nyregion/open-streets-nyc.html?searchResultPosition=1
https://www.nytimes.com/2009/02/26/nyregion/26broadway.html
https://resources.mpi-inf.mpg.de/departments/d1/teaching/ws12/ct/Braess-paradox.pdf