Or, if you’re someplace like 1850-1860s Chicago, you just lift the entire city up a few feet to create a new ground level. This too was for infrastructure reasons, but instead of transportation, it was for a sewer/drainage system.
https://en.m.wikipedia.org/wiki/Raising_of_Chicago
This then repeated itself in Chicago (and elsewhere). In the twentieth century, buildings were constructed over existing (and working) rail lines. These are existing example of using air rights to hide infrastructure to make the rest of the city more livable.
https://www.chipublib.org/blogs/post/technology-that-changed...
https://en.m.wikipedia.org/wiki/Air_rights
Even more recently, capping a highway was proposed by Cincinnati in their bid for Amazon’s HQ2.
https://cincinnatiideas.com/2017/09/25/how-cincinnati-could-...
Thinking about what I've seen so far I doubt it. What is the meaning of "public access" here? Gated, guarded and "operated" spaces, where you need to be paying customer for some venue, or buying a ticket?
The places themselves fenced/glass walled in to discourage suicides, stupid people throwing things down from high up, even if "only" a coin?
I mean, look at anything which comes to your mind right now, where people can go high above anything else where other people are below them. It varies, but often it is heavily fenced/walled to protect the people below.
And lastly, think of "reckless youth", and how groups/gangs of them tend to ... err ... impose dominance over places they consider "theirs".
Would you want to be there?
I don't recognize this gang thing, maybe because I don't live in a dense city (and don't recognize the attraction of it)
If you want a dense city, you want green roofs - with access. Land in a city is too valuable to waste on solar - stick that stuff out in the desert where nobody wants to be.
> Cut-and-cover highway tunnels
Take an existing dense city like Manhattan and build a new platform above the roads. Existing ground floor becomes basement, new platforms become park/pavements/plazas rather than for cars and trucks. Cities rise anyway - look at down town Seatle for a high speed example, but if you go to old cities in the UK, say Cambridge, and look at buildings 1000 years old, they're a significant drop down from today's "ground level".