] German scientists have shown that the changeover from
] free-flowing traffic to a traffic jam (in which cars on a
] highway are greatly slowed or halted, at least
] temporarily) conforms to the well-known physics of phase
] transitions, an example of which is the transition from
] water to ice. In other words, traffic jams are not random
] patterns, but are deterministic in nature; that is, when
] a parameter exceeds a threshold value--such as the flux
] of cars--then local perturbations can grow, possibly
] leading to jams, analogous to the nucleating effect of
] tiny ice grains in a body of water being frozen. Once
] formed the jam moves along the highway as if it were a
] kind of "solid," with identifiable edges and with a
] "vapor" of comparatively free cars in front of and behind
] it. The information gained in this sort of research, the
] researchers believe, might lead to more accurate traffic
] forecasts and could be used in future "intelligent"
] transport systems.

The physics of traffic jams