[43920]

Not to diminish OP’s project, but the stated goal of “know when each transit line has an upcoming train/tram/bus” is probably already achieved by https://transitapp.com/ - the default view when you open the app is a list of nearby transit lines, sorted by distance and showing the next departure for each.

[julesallen]

Like that there's no ads but it's a big no on the "data shared with third parties". Assuming this is how they make money? I'd rather wait 10 more mins for the bus I just missed.

[n4r9]

You can also bring up a station's departure board in CityMapper by clicking on its marker in the map view.

[Schiendelman]

And Apple Maps has a built-in nearby transit button that does similar.