Dumbo
For years while I was at the New Jersey (US) DOT I tried to promote more creative uses of the land under flyovers, such as skateparks, basketball courts, sculptural landforms, to no avail. They wanted nothing that would put people under them, out of liability concerns. I didn't get the logic. You're okay with having people drive under them and walk under them, but having them linger was a no-no. Such is the mental state of an overly-litigious society.
IN NYC, some commercial buildings were recently put up under the approach of the Manhattan Bridge. Of course, the land values there put a lot of demand on every square inch of real estate.