|Real-time bus data playback|
The data take awhile to load so it's been split up into pieces which are loaded in the background while the simulation begins. A progress bar will be displayed on top until it finishes loading, but the map will start showing the bus data that have been already downloaded.
It's easy to forget the scale of the system when you ride the same way every day. Just take a look, as it starts early in the morning with a lone 28 bus, and then explodes with activity as it reaches the morning peak, until the entire map is crawling with buses. And these are only the key routes.
(Tested in Chrome and Firefox; IE users may be out of luck).