  "Phantom jams," traffic blockages that arise without apparent cause, have
long frustrated transportation scientists. Herein, we draw a novel homology
between phantom jams and a related class of self-sustained transonic waves,
namely detonations. Through this analogy, we describe the jam structure;
favorable agreement with reported measurements from congested highways is
observed. Complementary numerical simulations offer insights into the jams'
development. Our results identify conditions likely to result in a dangerous
concentration of vehicles and thereby lend guidance in traffic control and
roadway design.
