Re:Doesn't slower speed increase congestion? (Score 1)

You're right to some degree, about predicting traffic flow being damn hard (I run traffic models for a living). There's a whole variety of software for predicting traffic at different levels of detail, from fairly coarse models of a region down to simulations that model individual vehicles (including driver behaviour etc). Unfortunately the very detailed models require huge amounts of data (intersection geometry etc..) and are impractical for modelling whole cities. Basically there's no way of modelling entire systems at the level of detail that we'd really like to go to. The strategic level models I use behave as you described, we look at where the traffic is generated, we look at the land uses that will attract that traffic. It's all then thrown on to the road network using variations on shortest-path algorithms, and we see what happens. Unfotunately, acurately predicting human behaviour is an exercise in futility, particularly when we're asked to predict 20-30 years in to the future.