Done, the definition was actually there all along after the parenthesis.
brt=yes/limited/no sounds like a good improvement to me.
@Kovoschiz I think the main criteria is if it is almost as important for the transport in a city as a subway or commuter rail would be. The BRT standard “leaderboard” is here: BRT Scores - Institute for Transportation and Development Policy
I think there probably should be an implication that anything that is “silver” and “gold” should be classified as BRT (and BRT certified and bronze can be “limited”). However, I am not sure they certify everything, I can imagine one needs to pay them and there were only several added rankings between 2018 and 2023, plus I am not sure if a ranking from ten years ago still holds.
I am for human-intelligible tags, so service is kind of meaningless to me (it can mean too many things). importance or quality would make more sense to me.
I guess there are two competing visions here - devise a very(?) detailes classification that would closely map onto a complicated reality vs. have a somewhat crude classification that would allow a simple distinction between very important routes, somewhat important routes and not so important routes.
Another way to put it is that that there is a phenomenon that is called BRT, it has physical manifestations, is kind of distincti and is unmappable in OSM currently. The question if if it should be mapped by its own thing or through some very generalized scheme.
For one, I think this should only apply to mass transit routes, no intracity routes.
Given how varied mass transit systems are across the world, I am not sure we can have a one-fits-all approach. Where I live, we have an excellent fixed-rail infrastructure so no need for BRT. Other cities are not as lucky, some are in between (Istanbul comes to mind).