Braess's Paradox
Braess's paradox describes a counterintuitive situation where adding extra capacity to a network (such as new roads) can actually slow down overall traffic flow, due to individual users acting in their own self-interest. The paradox was discovered by mathematician Dietrich Braess in 1968.
Background
Braess's paradox is a counterintuitive phenomenon in traffic flow theory: adding a new road to a congested network can actually make travel times worse for everyone, and closing a road can improve traffic. Discovered by mathematician Dietrich Braess in 1968, it arises because individual drivers acting selfishly (each choosing the fastest route for themselves) can collectively produce a worse outcome — a classic case of the "tragedy of the commons" in network design. The paradox is closely related to the Nash equilibrium concept from game theory. Real-world examples include Seoul, South Korea, where removing a 6-lane highway and replacing it with a park actually sped up traffic, and New York City's 42nd Street, where closing some streets reduced congestion. Understanding Braess's paradox influenced modern traffic management, ride-sharing algorithms, and the design of computer networks.