Google Maps entirely relies on the data given by transit agencies through their GTFS feeds, whether they be static or real-time. It doesn't do the same type of

Google Maps entirely relies on the data given by transit agencies through their GTFS feeds, whether they be static or real-time. It doesn't do the same type of calculation that the driving navigation does where they average travel times based on other users' movement. There are some other apps like Transit App that attempt to crowdsource the same data to reflect ETAs.