Elon Musk Digging Tunnels Underground

Seems like a fantastic idea. Without tunnels, we will all be in traffic hell forever I would say with tunnels you might still be in traffic hell. I also suppose we could also go above ground but that would require the air traffic control towers and flying cars might still be in the far future. But tunneling machines are here why don't we use them? I wonder if Elon Musk would design a 3D down house that way we can also live underground too lets bunker down instead of going upwards.

http://gizmodo.com/elon-musk-on-digging-big-ass-tunnel-we-have-no-idea-wh-1791803837