The development of urban parks and building space over inner city expressways is ferociously expensive and technically challenging. Rarely can it pass serious cost benefit analysis, let alone attract sufficient state and local funding. I can imagine several cities muscling their snouts into the federal for such projects, but the odds are against more than a handful getting built. But the conzultants should do well in preparing multi-volume studies and reports for such proposals.
Yet they do sometimes get built. Dallas did one a number of years ago over the Walton Walker freeway underpass. It's pretty nice.
If they can build a park on a concrete deck... they can put up something productive.
A nice office building.
Throw on a ‘green roof’ if they like.
The Old Main Post
Office: Before and After
For 20 years, the 2.5 million square–foot
facility has sat empty. Soon, it will take
shape as a sleek new office building.
“Fortunately, when the complex was mothballed by the United States Postal Service, original ornamentation, such as brass medallions, were put into storage. Other items, including lighting fixtures and the lobby’s revolving doors, were sent off-site to be refinished. The restored lobby is also expected to double as an event space in addition to serving as an entry point for the new Post Office, Schulze adds.”
https://www.chicagomag.com/real-estate/July-2018/The-Old-Main-Post-Office-Before-and-After/
Photos and details.
Sits above Interstate 290, the main east /west artery out of Chicago.
The original 1922 structure was a brick-sided mail terminal building, sited just east of the main building that spans the Eisenhower Expressway as it turns into Ida B. Wells Drive. Major expansion in 1932 added a total of nine floors for more than 60 acres (24 ha), or 2.5 million square feet (230,000 m²), of floorspace. Its footprint, as initially designed, would have blocked the proposed Congress Parkway extension; as a compromise, a hole for the Parkway was reserved in the base of the Post Office and utilized twenty years later.
https://en.wikipedia.org/wiki/Old_Chicago_Main_Post_Office