Hi Andrew,
[Understand gallery]
This native English speaker would not.
:)
gallery [...] 3: a room or series of rooms where works of art are exhibited [syn: {gallery}, {art gallery}, {picture gallery}] [...]
I think (3) is the most used meaning of gallery and it should be used in OSM in this way (e.g. museum=gallery, shop=gallery).
In fact, i cannot think of a half-tunnel in the UK. We generally don't have to worry about avalanches or stone fall, the main purpose of a gallery in CH.
As in the other example, it can also be used not to protect the street but just to expand the area above street level. Here an example of Zurich:
http://maps.google.ch/?ie=UTF8&ll=47.384956,8.537377&spn=0.000523,0....
But you're right, mostly they are built to protect the street from something. Still, the tag to describe it should be usable for both cases.
It might be worth asking somebody in the USA. There could be a dialect word which i as an British English speaker do not know about. Or they have extended the 5th definition above to include roads?
I think it's best to use a descriptive Key/Tag that anyone can under- stand. Especially if even you as a native haven't got a 'proper' word for it..
Regards, Thomas