Pretty much anyone of us that lives in a big city anywhere in the world has come across a phantom traffic jam. Basically a traffic jam that just appeared out of nowhere with no accident, lane closure, road construction to cause the traffic jam. You wait and wait to see what caused the traffic jam then all of a sudden everything clears up. Some ridiculously smart guys have come up with an actual equation on how and why this happens. Their equation and explanation are in the link below.