My cousin is a civil engineer with the NC DOT, he explained a few things about traffic flow to me, and one of the more memorable descriptions was the accordion effect. Traffic stalls, due to an accident, rubbernecking, debris in the road, just too many cars attempting to fill too few lanes or whatever, and the constant stop-start of traffic behind it gets magnified and radiates backwards, sometimes for many miles. It continues long after the obstruction of flow is removed. This is why you sometimes come to a dead stop in the middle of nowhere, and never even see the reason why. It was cleared hours before.
Yep...it’s all about time and mathematics