Looking at the way you've posed this bit of the question...
Some users may not care if there are only dirt trails and no sidewalks
on a path while other users in a wheelchair can only take the route if
there is 100% sidewalks so this metric would be more the most
...I get the impression that what you need isn't so much a way for users to see what everybody in the world thinks about the "walk-ability" (traverse-ability?) of a route, but a way for them to see what people who understand their situation think about the walkability.
After all, somebody on crutches or with a walking frame is very likely to have quite a different idea of walkability to somebody on a mobility scooter, somebody who has balance issues and needs to stop often or somebody able-bodied but who has to use a stoma-bag when they're out and about (so may need to stop and deal with it with very short notice). Their concerns are just different.
So how about we turn the question on it's side and look at it from that direction instead, and look at a way to match user concerns and then aggregate a walkability score only from closely matching people.
To that end, a user would be able to specify what their needs are. Being able to specify what their concerns are (not necessarily specific - just "can't be too far from plumbing", "need to sit often", "I move quite slowly", etc...) and see comments and an aggregate "walkability" score from people who closely match themselves...
It'd be worth having the ability to fill in specific details as well, but social proof like this works best when the user knows that the people who's opinions they're seeing have concerns that are close to their own.