May be underfoot. New hi-tech unpersoned drilling technology delivers underground building costs comberable with above ground costs in major cities. These automated drillers make it less expensive to build say new subway/rail lines than the above ground approach in populated corridors. These drillers were used in Boston's Big Dig (think Earthbound compatriot of the ISS boondoggle) whose roads are finally at long last opening up to the public. This drilling technology is yet another way in which technology changes all the linear rules.

What's also nice is that underground malls, e.g. Montreal, are also operationally energy efficient since the ambient temperature is always in the high 50s year round.