Video: Grand Central's Hidden Sub-Basement Has A 102-Year-Old Computer

http://gothamist.com/2015/10/15/grand_c ... hp#photo-1

Another look at it here:

http://hackaday.com/2015/10/17/retrotec ... -computer/

There's an interesting long article on the New York subway's signalling, and a video too.
https://www.youtube.com/watch?v=Mjx3S3UjmnA
It seems that safety is maintained by interlocking - whether mechanical or 300,000 relays depends on which part of the system you look at.

There's a simulator for Windows or OSX here:
http://www.nycsubway.org/wiki/NXSYS,_Si ... _Simulator

Here's the long article:
http://www.theatlantic.com/technology/a ... re/415152/