Saw an example of correct guardrail usage today, with the overgrown path that some other commenters were worried about.
(Lincoln Highway Hackensack River Bridge in Newark)
Let me tell you one thing, I would 100% rather ride on this overgrown sidewalk than on the shoulder of the 55mph highway without a shoulder. This is the official bicycle/pedestrian bridge crossing. I wasn't sure whether the bridge path is even open or exists, but it does and there were even other people using it. (There is a second mesh fence on the embankment side, more so to protect the bushes than to stop you falling over.)
And then take a look at this other beauty today:
(Weequahic Park Drive, New Jersey)
Correct guardrail usage AND perfectly maintained path! Alas, pedestrian only, but not a problem to ride on 25mph street. Proof that putting the guardrail before the sidewalk is perfectly possible, both legally and practically. (There is a lake down the embankment. Don't walk into the lake.)