How do I remove subway routes?

Solution 1:

If you'd like to delete an entire transit line, you can do this by clicking on the Transit overlay from the info panel in the top left corner, which allows you to click on transit lines to modify their name or color. There is also a "Delete line" button.

I found this somewhat confusing as there doesn't seem to be a way to access this from the Transit menu which you use to place lines and buildings, or add/delete/move stops.

Solution 2:

You do this by right-clicking at the station. If you have multiple routes at a station, you may not notice that the route is being removed, but keep on right-clicking, and eventually you get them all. Additionally, you can click and drag a route to a new station, which also applies to bus an rail routes.