Detours by Design: Optimizing Traffic Flow | SciAm
Braess’s paradox states that in a network in which all moving entities seek the most efficient route, adding extra capacity can reduce overall efficiency.
In this month's Scientific American, Linda Baker reports on applications of Braess's paradox to traffic flow in cities from Seoul to Boston.
Although Braess’s paradox was first identified in the 1960s and is rooted in 1920s economic theory, the concept never gained traction in the automobile-oriented U.S. But in the 21st century, economic and environmental problems are bringing new scrutiny to the idea that limiting spaces for cars may move more people more efficiently. A key to this counterintuitive approach to traffic design lies in manipulating the inherent self-interest of all drivers. ...
[D]rivers seeking the shortest route to a given destination eventually reach what is known as the Nash equilibrium, in which no single driver can do any better by changing his or her strategy unilaterally. The problem is that the Nash equilibrium is less efficient than the equilibrium reached when drivers act unselfishly — that is, when they coordinate their movements to benefit the entire group. ...
“Because selfish drivers optimize a wrong function, they can be led to a better solution if you remove some of the network links,” he [Michael Gastner, computer scientist at the Santa Fe Institute] explains. Why? In part because closing roads makes it more difficult for individual drivers to choose the best (and most selfish) route.
