Why traffic jams appear out of nothing

In 2008 researchers at Nagoya University put 22 cars on a 230 m circular track and asked everyone to hold a steady 30 km/h. Within minutes a stop-and-go jam appeared — no crash, no bottleneck, no reason. This is that experiment, with all the knobs exposed.

Scenario

Driver behaviour

The road

The intervention

The road

Every car is trying to drive forward. Watch for a band of red.
slow fast 🟥 brake lights on ▰ smart / auto-cruise car

✓Warming up…

Time–space diagram

Across = position on the road. Down = time passing. Each line is one car's path. Dark stripes leaning backwards are the jam. The steeper the lean, the faster the wave travels upstream.
↓ newest at the top, history scrolls down

Fundamental diagram

Every dot is one measurement from a virtual sensor in the road. Left branch = free flow (more cars, more throughput). Past the peak you fall onto the congested branch: more cars, less throughput.
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