A phantom jam is a localized wave of slow or stopped traffic caused by driver behavior rather than a collision, lane closure, or physical bottleneck. It typically starts when one driver brakes slightly, causing the following driver to brake harder, creating a backward-propagating shockwave of deceleration. These jams can persist for hours and travel upstream against the flow of traffic.
Heard on the job
The sensors show a phantom jam moving backward at about ten miles per hour near mile marker 42.
Also heard as
- shockwave jam
- traffic wave