Kirk, I thought this would be up your alley-- it reminds me of some of your past programs. Evidently there's a standard called "General Transit Feed Specification" which standardizes transit schedules as well as realtime position/timing data, This video is made from MBTA vehicle data (or maybe just scheduling+route data, I don't know exactly) for your city. Seattle also appears on youtube.
It's interesting how traffic can draw a sort of heatmap of the city.
http://www.youtube.com/watch?v=43T_9c_D_P0&feature=relmfu
That's pretty sweet!