INTERACTIVE EXPLANATION

Why do traffic jams happen?

One driver brakes. A slowdown travels through the road. Find out how a small action can affect everyone behind it.

Enable JavaScript to change the conditions and run the interactive experiment.

Follow the mechanism

MIT explains upstream-moving queues; the research team documents real ring-road experiments.

The model authors provide the acceleration equation, desired-gap equation, and meanings of the parameters.

These field experiments provide evidence for the phenomenon; they do not validate every setting in this playground.

A 600 m, one-lane ring; identical 4.5 m vehicles and driver parameters. The rendered road and cars are illustrative, not a scale drawing.
12–52 cars; desired speed 30–90 km/h; desired time headway 0.6–2.4 s. These are learning controls, not recommended driving settings.
Acceleration parameter a = 0.7 m/s², comfortable deceleration b = 1.8 m/s², minimum desired gap 2 m, speed exponent 4. These choices are not calibrated to a particular road.
Manual braking lasts 2.5 simulated seconds and applies a −4.5 m/s² limit. The application also caps deceleration at −7 m/s² and adds a 0.2 m spacing limiter. These are application additions to IDM.
Fixed 1/60 s time steps; nonnegative speed. The spacing limiter is a numerical guard, not a proof that all possible configurations are collision-free.
“Stopped or crawling” counts speed below 0.5 m/s (1.8 km/h). Time headway is a spacing preference, not an explicit reaction delay.
No lane changes, intersections, driver variation, or realistic crash dynamics. Each experiment is limited to 10 simulated minutes and 200 brake actions.

Independent subject review is pending.