Chiming in really late here, but just to throw a spanner into the works:
I would call it a sidepath. 
But as for sidewalks, some food for thought:
Road bridges are sometimes built with raised concrete sidewalks even if the connecting roads at both ends lack sidewalks. It’s easier and cheaper to build the sidewalk upfront than to later retrofit one into the bridge or build a separate pedestrian bridge. The sidewalks are unusable in the sense that they connect to nothing, and often there are signs that would lead us to tag them as foot=no or perhaps foot=emergency. But if you have the misfortune of your car breaking down midway along a highway viaduct, you’ll be more than happy to use the sidewalk rather than braving the travel lanes on foot out of principle.
Since a router won’t use these out-of-the-way sidewalks, the stakes are pretty low. But I think it’s still OK to map them, because we aren’t just mapping for routers – we’re also documenting the built environment. (And renderers get to render these sidewalks too.)