Why not Underground?

How do Urban Planners feel when confronted with ITA's most prominent question "Why go Underground?". How should they know the answer? After becoming better informed on Underground Space Use they should give equal responses when asked "Why not Underground ?". Because the "Above Ground" is loosing attraction, environment prefers Underground ! When it comes to the needs for hydro power, hydro engineers have no problem to think Underground, to connect tributary rivers with reservoirs or to supply water for purposes of drinking supply or industry. Why not underground? Because in most cases there is no alternative to solve the problem. What are the alternatives in Urban Mass Transport? Urban agglomerations are increasingly affected by mass transport systems as provided by municipalities when they are using either surface areas or elevated structures. Above ground structures evidently have negative impact to the environment and to the living quality of residents. Decisions for Above Ground Structures are similar in most cities. Underground solutions are considered to be too risky and too expensive.