Braess's Paradox
A city adds a fast new road. Does traffic get better — or worse?
by MindYourPuzzle
A paradox that has genuinely forced real cities to tear up roads.
Traffic flows from Start to End. There are two routes, each using one "wide" road (always ~45 min) and one "narrow" road whose time depends on traffic (roughly number of cars ÷ 100 minutes).
With drivers splitting evenly between the two routes, everyone's trip takes about 65 minutes.
Now the city builds a brand-new super-fast connector in the middle — so fast it's essentially instant (0 min) — linking the two routes, giving drivers a tempting shortcut.
Every driver is free to choose whatever route minimizes their own travel time.
After the new road opens, does everyone's commute get faster, stay the same, or get slower?