When two cars get into an accident the cars around them need to slow down to avoid hitting the cars involved in the collision. This causes a backup in traffic. People have often told me that traffic around an accident is caused by people 'rubber necking' or slowing down to see what is going on.
In my experience most drivers will quickly speed up as soon as there is open road in front of them, regardless of if there is a car off the road nearby. Have there been any studies that prove that people slow down just because there is a car off the road? Or is the traffic just due to the initial slow down filtering itself out?