There are numerous causes of traffic jams. On limited access highways, generally, it is not traffic volume alone that contributes to traffic jams, but a combination of that and other factors. Along a city street, traffic volume can contribute to traffic problems, as motorists get stuck behind lights, and one light cycle may be insufficient to allow all the motorists behind a light to pass through. Some of the causes of traffic jams are:
Accidents, which can block one or more traffic lanes
Disabled vehicles, which may obstruct traffic
Rubbernecking of accidents, disabled vehicles, stopped motorists, or other sights out of the ordinary
Construction, which may result in lane closures or the need to drive more slowly than normal
Events that draw large crowds
Inclement weather, leading motorists to have to drive more slowly or cautiously
Unforseen emergencies