I have not got a chance to play this awesome-sounding course yet (way too busy this last month), but here is my take, for what its worth. I would say one of these two things: "On or over sidewalks is OB", or "On or over roads is OB".
If the strip of grass between the sidewalk and road is IB and the sidewalk is OB, random shots could get rewarded/punished. For example: You shank your drive way right and land on the OB sidewalk...OB, too bad for you. I throw next, and shank my drive even worse, so I land 5 ft further right than you, but land on the strip of grass between the road and the sidewalk...I'm IB. This is not fair at all.
Again, I've never seen the land, but I would guess that the road is more clearly defined than the sidewalk (maybe true

). So I would end up saying "On or over the roads is OB". I know the course is young, but it might also be a good idea to eventually put this on a sign or the scorecard....that way everyone plays by the same rules (obviously lots of people will ignore the rules and do whatever they feel like, but at least there will be a clear intent).
Thanks to all of those who put in lots of hard work...I can't wait to check it out!