The only thing more frustrating than creeping your way toward the site of a bottleneck on the highway only to discover the accident is on the other side of the median are the times when you make it through and discover, as far as you can tell, nothing was holding up the traffic. Japanese researchers have now demonstrated that the "nothing" may in fact be the traffic crossing a threshold of density of cars on the road. Too many cars means that small slow downs by a few drivers equals up to big backups miles away.

It's 8:30 a.m., late rush hour, and Jim Murphy has a multibillion-dollar set of new tunnels beneath downtown Boston at his fingertips. So far things have been quiet, but should traffic get gnarly, as it so often does in this city of six-hour gridlocks, his console will automatically display the problem areas. Then he'll have some options: Zoom in on the jam through closed-circuit cameras; direct traffic with variable message boards; and, if things take a turn for the worse, override local radio frequencies.