Why does traffic sometimes form for no reason?

Why does traffic sometimes form for no reason?

Have you also noticed traffic jams with no apparent cause? No accident, no stalled vehicles, no lanes closed for construction. You inch along for tens — sometimes hundreds — of metres while waiting to see the accident which might have caused the jam. And suddenly, the traffic disappears and all vehicles speed up again.

Sounds familiar? What you saw is an intriguing phenomenon called phantom traffic jams, or jamitons. To best understand this, imagine being in a helicopter and looking over the Eastern Express Highway.

GIF Source

On a packed highway, a minor disruption to the flow of traffic can cause a chain reaction, like such: one car brakes slightly, and the cars behind it brake just a bit more to avoid hitting it. This braking eventually amplifying until it produces a wave of slowed or stopped traffic. This is a jamiton. And once it’s formed, it’s almost impossible to break it up again. You simply wait as the jamiton slowly evaporates at the downstream end, as cars break away from the jamiton. At the upstream end, however, the jamiton eats more traffic and absorbs it into the flow.

What one can do to avoid a jamiton –

  1. Maintain a steady speed and distance from the car in front
  2. Brake and accelerate smoothly
  3. Avoid sudden switching of lanes
  4. Curb your urge to "block the cheaters" (This feeling is real.)

Now you know what to do the next time you approach a jamiton on your way to work!


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