[Windflier]

The development of urban parks and building space over inner city expressways is ferociously expensive and technically challenging.

Yet they do sometimes get built. Dallas did one a number of years ago over the Walton Walker freeway underpass. It's pretty nice.

[null and void]

What could possibly go wrong?

(EVERY time I drove on the bottom deck, I'd look up and wonder what this would do in an earthquake. EVERY TIME. Now we know...)

[Rockingham]

There is also the High Line park in NYC. Yet few cities now have the physical structure and property values necessary to such pronects.