phantom jam

plural phantom jams

1. automotiveA slowdown in traffic that occurs without an apparent reason.

   The leftover phantom jam might be miles away from its orgin.

   2001 August 25, Sherman Cahal, “ARTICLE: Traffic: Stuck in the Maddening Crowd”, in misc.transport.road (Usenet)

   3 more examples

   Eventually, the phantom jam always dissolves. Sometimes the phantom jams are large and sometimes they are small.

   1996, Achim Bachem, Dietrich E Wolf, Michael Schreckenberg (editors), Traffic And Granular Flow, page 76

   One of the most affected problems is the behavior of freeway traffic, which includes the appearance of "the phantom jam."

   2003, Elsevier Limited (publisher), Control in Transportation Systems ... a Proceedings Volume from the IFAC Symposium, page 335

   Finally, when interpreting accidents as events “out of thin air”, there are, in fact, phantom jams.

   2012, Martin Treiber, Arne Kesting, Traffic Flow Dynamics, Data, Models and Simulation, page 569

2. automotiveA traffic jam that appears at a distance on a highway, but in reality is an optical illusion.