I have noticed some short tunnels/pipes in the forest from one side of the railway to the other, cutting through the embankment.
These tunnels contain no water (it might be a temporary situation), so my guess is that they are meant for animals.
I have no idea of what tags belong to it. I don’t think it’s a highway or a path, because it doesn’t connect to anything, and could be misleading - some of the tunnels have 1m diameter.
The closest would be a waterway, but with no water.
Currently, I marked them with custom tags: barrier=crossing, diameter=1, similar to the stiles, although stiles and gates are parts of the barrier.
Well 1 meter in diameter isn’t much, what kind of animal are supposed to pass through there, mooses wont fit and neither will most deers. I would say waterway=drain(?) and diameter/width=1meter.
I saw a lot of rabbit tracks going into the tunnels.
There was another tunnel probably meant for animals 2m wide, with square cross-section, that was more useful to humans than the others (waterway would mean it’s unusable as I understand the tag). Roe deers (seen nearby) could pass through it.
The question is not about the diameter, or this very case, but about tagging that kind of tunnels overall.
For the smaller tunnels, I would say man_made=pipeline http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dpipeline
with something like type=animals, and location=underground, diameter=1 etc?
Though I don’t know how that will mark the ends of the pipe on the map.
For the ones big enough for a person, I would use highway=path and tunnel=yes. Paths don’t always have to be joined on to something else.