h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Recently, it has been proven that a jam several hours ago may affect you. When a small jam forms, it immediatly heads backwards, against traffic. This is due to two things
1) People, like ants, are always in a hurry. If they are not in a hurry to do something, they are in a hurry to find something to hurry about
2) People in a hurry naturaly enter a trance like state, where if anyone is traveling at any speed slower than theirs, they will move to within 2 electrons of their bumper. Cars are not designed to do this, and doing slow takes considerable slowdown time. See rule number 1 with the next car behind them.

Thus if there is a jam, it is not worth looking out your window to see what's holding up. It is possible that it was caused by a person who, serveral hours ago, and several miles away, drank a pan-galactic gargle blaster in the middle of the road.