Pretty much this, if its sub-5 story slum (aka most US cities & nearly all suburbs) overlaying rail is a bandaid. The city was built wrong in the first place, a

Pretty much this, if its sub-5 story slum (aka most US cities & nearly all suburbs) overlaying rail is a bandaid. The city was built wrong in the first place, and needs to gain density, rail can keep a dense city economically viable by providing reliable, rapid transit. There is no good transit solution for suburban sprawl.