What If a City Had No Red Lights? We Simulated 2 Towns | What If, Calculated #01

What if every traffic light stayed green — would a town actually get faster? (all-green intersections · what-if traffic simulation) We built two fictional towns, a big city and a countryside town, and calculated what happens when no light ever turns red.

This episode's page (run the simulation yourself, explanations, sources): haccha-meccha.com/en/moshimo/01

The two towns are fictional, built for this calculation: a "big city" (1 km², 25 intersections, 900 cars leaving in a 5-minute morning rush, 24 cars per km of road) and the "countryside" (a 1.5 km square, 9 intersections, 100 cars, 2 cars per km of road).

The answer depended completely on the town. With cars that never collide, the countryside got 24% faster, while the big city came out almost tied with normal signals. Then we added a rule that one in twenty near-misses becomes a real crash: the big city had 27 crashes, only a third of the cars arrived, and even the cars that did arrive took 22% longer than with signals. Under the same rule, the countryside had 2 crashes and also ended up slower than with signals (+76%). Traffic signals turned out to be the safety device of a crowded city.

How we calculated: Fictional towns. First we compared everything with cars that never collide. At an intersection, the car that came first goes first; a car that stopped takes a 2-second look before moving off (based on research showing a start-up loss of about 2 seconds). Then we ran it again with crashes: one in twenty near-misses (moments that need hard braking) becomes a crash (from Bird's ratio in workplace safety). A crashed intersection is closed for 10 minutes and cars detour (the 10 minutes is our own setting). Even on green, a single lane can only send about one car every 2 seconds through an intersection (a basic traffic-engineering value). Cars drive on the left, as in Japan. Each number is the middle value of 3 runs with different random seeds.

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