No abstraction, the biggest flaw with your idea is the massive amounts of physical area you are calling into play. You're addressing the aesthetics of railroad tracks and highways that cut through places, but you're missing why they are so destructive. A few hundred feet add up very quickly in an urban environment. You're focusing on aesthetics and green space, but there are ways besides open space to achieve these goals.
In that same grain, I think that type of 'go for it' innovation would require the ability to stop, remove, and reboot when necessary. Something that would require people to relinquish ownership to the planners/central org. And who pays for these things? As sad as it sounds.. its like 'whats the business model?'
A little off topic, but just noticed that the signage for the Mermaid ride is kind of . . . gruesome. They've got Ariel tacked up on the front of a shipwreck, almost in a crucified manner as the wooden masts of the shipwreck look almost like a cross. Plus, this was how Ariel's mom died . . . she got smashed between a ship and some rocks on the coast! I get it from an artistic viewpoint, I guess, if you want to equate Ariel with wooden women nailed on the front of ships, but you can bet that little girls will wonder if Ariel is stuck or hurt, given how she looks.
Ariel, the young mermaid sitting on a rock looking at Eric's ship is Ariel's story, this monstrosity reduces Ariel to a generic mermaid, a smiling unaware bimbo tacked on the front of a shipwreck, oblivious to the world around her because she is reduced to an inanimate object.
I bet if you took a picture of Ariel face on, you could get a shot that looks like she is up on the cross. Somebody tell me I'm crazy, but this is just an awful artistic choice, I'd bet real money that the sign is removed and replaced with something less . . . offensive. Wonder if they'll realize that the thing on the balcony is a trellis which had vines on it in the film.
I understand the concept of a greenbelt and green space. But green space is not really a big issue anymore in American cities. Simply wrapping a project in green space does not make it better. Olmsted advocated and designed his parks with grade separated parkways, just what you're suggesting except for carriages. The interstates were also designed with green space along the roads, and this includes belt interstates. But they were destructive to the urban environment well before the expanded into their green space. Its also not the specific vehicle that causes the issue. It's the barrier that is created. This is why light rail is so desired as it fits into an urban area or green space, not cut it apart.
Greenery is not equivalent to green spaces and parks. Even if there was no transit, a big hill covered in plants running through a city would still have a deleterious effect on the urban fabric. It doesn't matter what it is for or how it is composed; the problem is the spreading out of the urban environment.
The monorails do not cut apart because, excepting a few pylons, one can see and walk through their route. There is no barrier like your propose. This is also why elevated trains were built, even into farmland to encourage growth. While they have a blighting effect, an elevated train maintains close proximity for pedestrians that is removed by having something built onto ground, either level with the street or on an embankment.
The utilidors have prevented larger landscaping in the Magic Kingdom. You'll need a larger structure for supporting larger landscapes. You're just moving the issue around.
It's not the trees that have the deleterious effect, it's the berm. The berm. That is what breaks apart the urban fabric. It is a big obstacle for the purpose of separation. The berm is the problem regardless of what it holds or how it is made.
A utilidor under a building is called a basement. If you're just building basements then that isn't much of anything special. If they are going under the ground level, then they are something different, and those areas would be landscaped. To support that load, you need a structure. So instead of building the structure for the transit, you're building it to hold up the city.
