That I can remember right now, I&#x27;ve taken the subway&#x2F;train in New York, Boston, Chicago, London, San Francisco, and DC. Some of them are really great, others are not (looking at you, Green Line on the Boston T). Building these systems was almost certainly a great idea at the time.<p>My main point is that technology is now changing and I think that de-centralized mass-transit through fleets of automated cars is close at hand.  And it can use the infrastructure that we already have. So building super-expensive fixed-line transit infrastructure within cities is not a good investment anymore.  Even more so when you consider the turnaround time from initial planning to opening to the public is probably a decade.