This sounds like you need motion capture capabilities rather than video. Think "Lord of the Rings" and Gollum. Or to bring it to the present day, "The Adventures of Tin Tin". Both used motion capture to generate the actions of 3D models.
Nah, forget it. What you describe is hardcore 3D tracking and that of the analytic kind requiring multiple cameras. There is no way whatsoever to reconstruct such complex data from just one camera mounted randomly somewhere. In that case you could just as well draw some random paths freehand and it would be just as correct/ incorrect - whichever you prefer to a call it...
If you have a locked off camera looking at a street scene and you want to track the movement of people on the ground you'll only have luck if the street scene isn't very crowded. You could try After Effects Point tracker to track individuals one at a time, or Mocha, to track people one at a time. The other option would be to use Camera Tracker from the Foundry.
All of these will just give you the ability to tie a layer's position to movement. Then you'd have to work up an expression based on velocity to control opacity to automatically detect when the layer was moving. Once that was done, the layer's movement could be turned into a path which was applied to another layer. The path could be stroked with a color and the in and out points of the stroke tied to the movement of the layer with another expression.
If I new better what you were trying to achieve or you had an example maybe I could give you better ideas. The only thing I can say for shure is that you'll need to do a bunch of tracking, a bunch of tweaking to those tracks and a bunch of experimentation with expressions to get what I think you want. If what you want is accurate data based on movement then Mylenium's right, a single camera and AE isn't the right tool. You'll need to do some research on motion capture.