phantom jam

a ring road. every car drives at the same speed limit. nobody brakes for a reason. yet a jam appears out of nothing and crawls backwards around the ring. this is the nagel-schreckenberg model: cars speed up, then randomly slow down with probability p. that tiny randomness is enough.

jams on road: 0  ·  avg speed: 0 cells/step

watch the slow patches: they drift against the flow of traffic. the cars move forward, the jam moves backward. same physics as real motorway phantom jams.