[GenKreton]

That's not a traffic jam, that is congestion. Speed differentials and sudden braking especially cause standing waves which lead to traffic jams. This is modeled by a compressional wave. Regardless of the initial velocity there will be points of no movement in a compressional wave. As your link clearly illustrates maintaining a herd at a constant pace alleviates any chance of traffic jams.

Anyways, if everyone were driving the speed limit, things would have been fine. In fact, the view from the bridge shows the side abiding by the posted limit is about as congested as the side speeding!