The physics of traffic jams

Ever wondered why traffic slowdowns can persist for hours on a certain stretch of highway, only to end abruptly once you move a little further down the road?

Theoretical physicists have studied such questions, and they've found answers, Wall Street Journal science columnist Sharon Begley reported recently. (Someone generously posted the entire column onto Usenet for non-subscribers.)

Theoretical physicists began delving into traffic in the late 1990s, siccing equations of nonlinear dynamics and models of cellular automata (yes, they are as opaque as they sound) on such mysteries as why stop-and-go traffic can, for no evident cause, start zipping along again. Although the research has yet to produce a practical way to eliminate congestion, it has shown that there are empirical causes for such miseries as traffic slowing to a crawl even when there is no accident or rough pavement in sight.