Percy Johnson-Marshall was our City Planning Professor at The Edinburgh University.
Today his words are still vivid on my mind. For example, he said that ''when a city reaches a certain size it presents more costs than benefits''. In relation to metro systems he said that ''when a city needs a metro system, what you need is a new city''.
Nowadays, the Curitiba city municipality (where I live, in Brazil) is debating on the need to build a metropolitan rail system.
As far as I know metro systems implies in population agglomeration, and all its costs associated with urban quality of life.
In my opinion a metro system in itself does not make people happyer. It just transport them faster to their destinations than other modes.