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.

Add another study to the growing body of evidence that red-light cameras cause more accidents than they prevent. University of South Florida researchers found drivers are more likely to attempt to stop abruptly at camera intersections than otherwise, which results in a significant increase in injuries from rear end collisions. Red-light cameras are designed to snap a photo of a cars license plate if the driver moves through the intersection under a red light. The theory should hold that if drivers know theyre being watched, theyll be less likely to run the lights.