CA: I had heard the Arco Towers (long since renamed) but The Hotel Bonaventure might have done it too - any of the newer high-rises (and that's the majority of them) that were built past the late 1950's when the subway tunnels were "abandoned forever" could have done it. You'd need an old system map and overlay it with the current landscape on top.
And Politicians would LOVE to recycle the old tunnels if the routing is right, and I can point out exactly why - A Politician's favorite song to sing is "Me, me, me, me, meeeee! I, I, I, I, Iiiiiiii!!" A politician and a hot mike and a live camera are Really Hard to seperate.
The Pol wants to get something done DURING THEIR TERM that they can attend the Grand Opening of, point to, and say "Look at it! I got this done for you! Re-Elect me to another term, and there are even more wonderful things I can get done for you!"
You can rehab and open an old existing tunnel in a matter of three or four years - even with major rework needed in spots you already have a stable tunnel there, entrances and exits that connect to an established ROW, rudimentary ventilation and lighting utilities in place, often the old tracks are still good enough to use for transporting materials in and out, etc. There will still be a fair amount of 'pouring concrete' before it's all done.
Dig the same tunnel from scratch, and now you are talking 10 to 20 years from groundbreaking to opening, and the mystery geology of the route. No politician is really willing to push for it if he won't see the benefits during his (or her) term in office. And they really don't want to hand that golden moment to the next person in the office.
--<< Bruce >>--