Adding a road can make traffic worse. Not as a figure of speech, but as a mathematical result. In 1968, German mathematician Dietrich Braess showed that adding capacity to a network can increase travel time for everyone when each driver picks the route that is fastest for them alone. The classic setup: - 4,000 drivers travel from Start to End - Route 1: a congested road where time = T/100 minutes (T = number of cars), then a fixed 45 minute highway - Route 2: the same two roads in the opposite order, 45 minutes fixed first, then T/100 - At equilibrium the drivers split 2,000 and 2,000, so every trip takes 20 + 45 = 65 minutes Now add a free shortcut, a zero minute link joining the two congestion-dependent roads. - Every driver sees that the variable road beats the 45 minute highway - Everyone takes variable road, shortcut, variable road - Each variable segment now carries all 4,000 cars, so the trip is 40 + 0 + 40 = 80 minutes - No single driver can improve by switching back, so t...