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More Roads, More Traffic…?

Does Destroying Highways Solve Urban Traffic Congestion?

 

Two parallel roads with common endpoints generates less traffic than just one road. It seems simple, but it’s not. It goes far deeper than more roads equal less traffic because it’s imperative to address how humans make their route choices to minimize their travel time while neglecting that of neighboring cars. Matthew Philips article details the true effect that more roads has on a network and that this recent decade’s addition of roads has often led to increased traffic and congestion. Also suggested in his article and evidenced by Seoul, Korea, the demolition of a profound freeway in the heart of the city has alleviated a significant margin of traffic. While this and the linked article both detailed the effects of the removal, they failed to explain why it had this effect on traffic congestion.

 

It turns out the traffic levitation can be attributed to Braess’ paradox which suggests that added roads can impede overall traffic flow through them. A Nash equilibrium of a road network is simply the equilibrium distribution of drivers across a road network in real life. Braess’ paradox occurs when the Nash equilibrium of a road network doesn’t match the most efficient flow through said network. The introduction of a new road leads to a brand-new game structure and subsequently a prisoner’s dilemma. This is because drivers act on their own self-interest and not on the interest of the network as a whole. Generally, when the demolition of a road is successful for traffic mediation it is because the preexisting road was overly used by drivers and dispersing routes and Nash equilibrium quantities across the city ends up decreasing average trip time.

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