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Added except for the aerial tram since that's an outstanding issue. Probably should make a dedicated thread for it.
Regarding the system abbreviations and names, a few things I might as well document:
- commuter rail systems generally use the railroad's official reporting mark (e.g. TRCX is Tri-Rail, hence usatrcx)
- urban transit systems tend to use the abbreviation for the agency that runs it if a simple one is available, but with extra added to disambiguate if there are multiple systems with the same owner (e.g. usarta and usartalr, the heavy and light rail services, respectively, of the Rapid Transit Authority in Cleveland)
- unless another obvious abbreviation is available streetcars are often the first letter(s) of the city name + sc
- if a system specifically serves a particular airport that airport's IATA code gets used (e.g. usaatl for the ATL SkyTrain), and on the flipside I would
avoid using the airport code if airport is not involved in order to avoid confusion (so no "pdx" unless it's something serving Portland International Airport)
Ultimately though this is going to be less formulaic than it is for roads, so there will be cases where something has multiple reasonable possibilities. In which case the important thing is to pick one and use it consistently.