I’ve been questioning how I’ve created sidewalks surrounding my campus. For instance, there is a 5 lane bridge going over a river and the bridge has sidewalks on each side. As I have it currently drawn (https://www.openstreetmap.org/#map=19/43.12416/-77.63249) it looks like there is a road bridge and the two small pedestrian bridges spanning the river next to it. That can’t be the right way to do this. Do you include separate pedestrian ways normally, or only if they are not adjacent to a road, and then just tag a road as having sidewalks. I’m not sure what way to do this and have walking directions still work. Thanks.
You could add a man_made=bridge. Since the last update of the standard rendering style on osm.org, those “bridges” are displayed.
There is a footway and cycleway on the motorway bridge over the Rhine river near Koblenz, and it looks like being on a separate bridge: https://www.openstreetmap.org/#map=18/50.41013/7.57418
Also the foot/cycle/motorbike pathes on the Victoria bridge over Perak river near Kuala Kangsar: https://www.openstreetmap.org/#map=17/4.83917/100.96131
That is, the problem exists in several places over the world… It will take some time to find all such places and get them tagged as suggested by escada.
When the Germans would start a “week assignment”, all those bridges will be added in no time 
I’ve been doing this for half a year or so in Belgium, whenever I encounter this situation. So it is just a matter of time, as with all things OSM