[Tagging] Are tunnels only below ground? (Was

[Richard Bullock]

> I concede.
>
> In fact my OLD Encyclopadia Britannica states that a tunnel is excavated
> underground and a "cut and cover" is not truly a tunnel.
>
> So the question now is how to tag an above ground "tunnel-like" structure
> to properly indicate it's characteristics, that is "completely enclosed on
> all sides, save for the openings at each end".
>
We don't *have* to stick to dictionary definitions here when tagging, as 
long as the meaning is clear;

If it walks like a duck, talks like a duck, then define it to be a duck.

I wouldn't hesitate to tag a cut-and-cover structure as a tunnel in OSM.

A passageway through a building (but, say, without being inside that 
building) is, to all intents and purposes, a tunnel. It doesn't necessarily 
matter whether the "tunnel" is through a brick-built structure instead of, 
say, a man-made earth embankment or natural hill.

By all means expand the tunnel key like others have done with bridge=* to 
describe the tunnel properties;

e.g tunnel = cut_and_cover / tunnel = avalanche_tunnel etc.

But I think the key here is that tunnel=yes should be allowable to get the 
basic meaning across without an editor requiring to be an expert in tunnel 
construction.

Of course there will be edge cases, but we don't have to go and invent a 
million new keys to describe similar, but not identical, classes of object.