clay_c
Where did you find that railway=light_rail is usually used for metro lines? Common usage of the term "light rail" in North America includes street-running railways. There are examples across the US and Canada, like in Portland, Minneapolis and Calgary. I'm not sure what standard you are referring to here.

The San Francisco Municipal Railway has three different street railway services: the "Muni Metro" (a "premetro" system as they call it in Europe), the heritage streetcars (old restored trams from around the world), and the historic cable cars. The Muni Metro and heritage streetcars share a common gauge and electrification, and even use the same maintenance facilities, but certain tracks are streetcar-only and cannot support heavier Muni Metro vehicles. In North America, at least, we tag the underlying ways according to the heaviest vehicles they can support. Sometimes this even results in parallel tracks with different classifications [1]. This is a reflection of ground truth, not a tagging error.

As a resolution to the StreetComplete issue: would it suppress the quest if the crossings were tagged `railway=tram_crossing` and `railway=tram_level_crossing` instead? I believe those are seeing increasing usage elsewhere.

[1] https://www.openstreetmap.org/#map=19/33.14171/-117.16051