I would love to see this come to more cities. I live in a major north American city where public transportation is run by the local government. They have an official transportation app, but it's a buggy mess that's just a wrapper for the phone browser. It features "real time" (their words) route tracking, but as I quickly found out, the busses that move along the map aren't actually representative of the real busses…
https://developers.google.com/transit/gtfs/
https://developers.google.com/transit/gtfs-realtime/
I'm a bit curious which city you live in, because the majority major cities(at least in the US) publish both GTFS and GTFS real time. This is how Google(and other applications) gather the data. Does Google Maps provide real time data for transit? If not, you may want to get in touch with your cities transit service and inquire why not. I was part of a team that did GTFS(not real time) for a small area, and it was not incredibly expensive. Most of the data the transit service already has and its usually just a matter of doing some transformations on the data into the new format.