busway on under-tagged roads

[dabreegster]

busway on under-tagged roads

[BudgieInWA]

I had a thought about how to understand the busway tag in the absence of proper lane count tags. I am fairly confident that we should be trying to understand lanes:* (the lane count for different types) and *:lanes (access restrictions, specified per lane) first, and laying busway tags on top of that. The first two schemes are precicely defined with clear defaults, whereas the busway scheme only tells us about the presence of a busway on one or both sides, and leaves a lot of details unspecified.

Anyway, the idea: When the lane counts are not tagged, instead of guessing lanes=2, we actually want to guess lanes:car=2 (not a real tag, but counts the number of "normal" lanes). We normally guess lanes:bus=0, unless we see a busway tag which implies lanes:bus=2 (or 1 or whatever). Then, if we don't have a lanes tag, we get guess the total lanes to be lanes:bus plus lanes:car. If we have lanes and busway then we guess lanes:car to be lanes - lanes:bus. The guessed lanes:car value - as distinct from lanes - is a way to distinguish between the cases where we need to add lanes for a busway, vs convert existing lanes to bus lanes.

[dabreegster]

https://www.openstreetmap.org/way/39597033 uses multiple schemes