Digging out extensive underground road infrastructure is very expensive. Ask Boston residents if they'd like to do a second Big Dig on a much larger scale to bury the streets.

Elevated walkways would be vastly cheaper, but still infeasible on any current budget. You would end up having to rebuild the lobby of most buildings to be on the second floor, and probably turn the first floor into parking. It feels like one of those utopian ideals from the 50s or 60s that came out before people started thinking about the money.

On the other hand, the downtown area of Chicago was raised up from natural ground level in the 1850s.

Seattle was raised in the 1880s.

A portion of Atlanta was raised in the 1920s. They actually did rebuild new lobbies on the upper floors, and a lot of the old storefronts are still intact down below.

i lived in boston during (the tail end of) the big dig and remember the excess costs were largely due to corruption and maybe some incompetence. look at how much nicer it is there because of it. i'd vote for it again in a heartbeat (with some better processes and oversight of course).

but yes, underground infrastructure is expensive (maybe the boring company will help drive equipment costs down), but we're a rich nation and we want nice things. i think we can do it if we want to. plus, it creates working class jobs and that makes the economy go 'round.

Or the rain...