Here is a good page with info about various European and American cities' systems and quite a few technical details about them: http://www.douglas-self.com/MUS

Here is a good page with info about various European and American cities' systems and quite a few technical details about them: http://www.douglas-self.com/MUSEUM/COMMS/pneumess/pneumess.htm http://www.douglas-self.com/MUSEUM/COMMS/pneumess/pneumess.h...