Earlier quoted context omitted.
Have you lived in a city with a subway? Give it a few years, and all the stuff is nearer the trains stops anyways. The train is rarely out of the way.
I currently live in both New York and Los Angeles. The subways in NY work because of density, but they won't work in LA. Lightrail can be improved, and more lines added, but you're not going to get NY mobility in LA with trains alone. Not until someone solves the last-mile reach with something other than cars.
Transportation determines density.