From a reader in response to brilliant-stupid tunnel idea:

It’s not ridiculous if you built the tunnels like they built the tunnel (utilidor for you Mouse geeks) under the Magic Kingdom in Orlando. They built the structure above ground and then covered it with earth, and built the MK on top of that.
Wikiproof: http://en.wikipedia.org/wiki/Magic_Kingdom#Construction
How hard would it be to basically roof over and pile dirt on top of the existing Interstate Highway System? Certainly not impossible. And you’d realize huge savings in lowered maintenance costs? Plus, the CO2 released would feed the trees you’d plant on top!

Where’d I put that column?