Lookit. It's just vaporware, and there are real usability issues...
But this SkyCycle concept, to put a network of trails above rail rights-of-way in London, I think has some limited applications in lots of places. https://www.fosterandpartners.com/projects/skycycle/
@bikepedantic I can see the value, definitely—especially if it’s not built above a bunch of exhaust. Definitely issues to be dealt with: how steep the on- and off- ramps are and how many there are, along, of course, with what bicycle infrastructure exists between those ramps and between these highways.
@bikepedantic True. Albuquerque does a pretty good job with frequency of ramped overpasses over Tramway (there’s one of these at every major cross-street with decent bike lanes), *but* (and this is key) many of them have sharp corners that make the bike all-but-stop around the corner. There’s enough space that they could’ve built them better, but it’s obviously not very urban up there either.