How do traffic waves travel downstream (traveling in the same direction as the flow of traffic)?
i.e. How can the flow of traffic in a particular location be affected by the flow of traffic behind that location?
I think I understand how traffic waves can travel upstream (against the flow of traffic). It can happen in many ways, e.g. A car in front applies the brakes, so the car behind also brakes, then the one behind that etc. This information can travel faster than the flow of traffic, so this wave of braking travels upstream down the motorway, sometimes for miles.
However, I cannot workout how a traffic wave could travel downstream. Can somebody please provide me with an explanation as to how this could happen?