i saw a commercial for this on PBS the other day (nerd alert), did some google research and think it's pretty amazing. stockholm (also london, oslo and singapore) introduced a trial congestion tax to reduce the amount of cars on the roads and paired with IBM to make it technologically seamless. "The goal was not only to reduce congestion, but encourage ancillary benefits, such as improving public transportation and alleviating environmental damage." in the six month trial period, traffic moved down nearly 25%, 40,000 more people ride on public transportation everyday and greenhouse gases dropped 40% in the inner-city. the tax was reinstated by swedish law in july 2007.