(*) Brings the problem of ambiguity I'm not even sure, if 'gallery' is understood by an English native (it's 'Galerie' in German).
This native English speaker would not.
gallery 1: spectators at a golf or tennis match 2: a porch along the outside of a building (sometimes partly enclosed) [syn: {veranda}, {verandah}, {gallery}] 3: a room or series of rooms where works of art are exhibited [syn: {gallery}, {art gallery}, {picture gallery}] 4: a long usually narrow room used for some specific purpose; "shooting gallery" 5: a covered corridor (especially one extending along the wall of a building and supported with arches or columns) 6: narrow recessed balcony area along an upper floor on the interior of a building; usually marked by a colonnade 7: a horizontal (or nearly horizontal) passageway in a mine; "they dug a drift parallel with the vein" [syn: {drift}, {heading}, {gallery}]
Looking at these definitions, you can see a link to the concept used in CH for half-tunnels, but in UK the word Gallery is not used for this. 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.
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?
Andrew