Have you ever been driving on an interstate highway when traffic suddenly slows to a crawl? You inch along for many minutes while waiting to see the accident which must have caused the jam.
At the same time you also curse the “rubberneckers” who are causing the whole problem. But then all the cars ahead of you take off at high speed.
The jam is over, but no accident, no police cars, nothing. WHAT THE HECK WAS THAT! A traffic jam with no cause? In the rear-view mirror you see all the poor saps behind you still stuck in the jam.
But why? If all those people could just speed up at the same time, the whole traffic jam would evaporate. Why don’t they ever do that? What caused the mysterious slowdown in the first place?
Andrew Marr explains the phantom traffic jam from a cherry picker and then on a computer graphic.