fairness · paradox
Braess's paradox
Drivers are going from home to work.
Drivers choose routes from home to work. Travel time on each road increases when more cars use it. A new shortcut is added. Drivers can now take the shortcut.
Cars are choosing routes. What happens when a new road is added?
Before the shortcut, drivers split between two reasonable routes and travel times stay moderate.
The new road looks faster to each individual driver, so many switch to it.
The extra traffic slows the shared segments enough that every driver takes longer than before.
Adding a road that everyone wants to use can make the whole network slower. That is Braess's paradox.