Why adding a road can slow every driver down: Braess's paradox
30seconds
You would think a free shortcut can only help. In 1968 the mathematician Dietrich Braess showed it can make every driver slower.
In our four-road example, 4,000 drivers take 65 minutes each. Open a free link between the middle points and each driver is tempted to switch, because the zig-zag is quicker for the person switching. When everyone does, every trip takes 80 minutes, and no one can improve alone.
Open and close the shortcut and watch it happen.
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