Jams,
Here is the link to the program about underground cities. I watched the latest one about L.A. yesterday and how they did away with their subways and sold them to the car and tire companies who immediately ripped the tracks up and closed them down so people had to buy cars. Now L.A. is the 2nd largest city, has the worst traffic, and the dirtiest air and no plans for a subway. I believe they said it is the only major city in the U. S. without some kind of subway or train system
http://www.history.com/cities-of-the-underworld
Ron