MTA Bus Time now supports GTFS-Realtime.
TripUpdates, VehiclePositions, and Alerts are available at the following URLs:
https://gtfsrt.prod.obanyc.com/tripUpdates?key=<YOUR_KEY>https://gtfsrt.prod.obanyc.com/vehiclePositions?key=<YOUR_KEY>https://gtfsrt.prod.obanyc.com/alerts?key=<YOUR_KEY>
Where <YOUR_KEY> is your MTA Bus Time developer API key (required). Go here to get one.