Adding capacity to a network can worsen overall performance when users independently optimise their own routes.
Braess's 1968 result, confirmed when Seoul demolished the Cheonggyecheon expressway in 2003 and traffic improved. New York closing 42nd Street on Earth Day 1990 produced the same effect.
In practice
- A city opens a new bypass and finds journey times unchanged, because drivers who had avoided the route return to it.
- A team adds a second checkout queue and the total wait rises, because the queue is now worth joining.
- Further reading
- Wikipedia
- Subject
- Networks & Collective Behavior
- Essay
- How connections shape what crowds do