Traffic jams without bottlenecks—experimental evidence for the physical mechanism of the formation of a jam

A traffic jam on a highway is a very familiar phenomenon. From the physical viewpoint, the system of vehicular flow is a non-equilibrium system of interacting particles (vehicles). The collective effect of the many-particle system induces the instability of a free flow state caused by the enhancement of fluctuations, and the transition to a jamming state occurs spontaneously if the average vehicle density exceeds a certain critical value. Thus, a bottleneck is only a trigger and not the essential origin of a traffic jam. In this paper, we present the first experimental evidence that the emergence of a traffic jam is a collective phenomenon like ‘dynamical’ phase transitions and pattern formation 10 Author to whom any correspondence should be addressed. New Journal of Physics 10 (2008) 033001 1367-2630/08/033001+07$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft