Via Planetizen, here’s a mostly fun and I think actually educational game from the University of Minnesota where you have to serve as traffic engineer, setting the red and green lights to keep traffic moving smoothly. As has been said, you don’t get to do anything like put in buses, which would really reduce congestion, but there’s no reason for fans of sustainable transportation not to support smoothly functioning cars, insofar as they exist, or transportation-related flash games.