[davismwfl]

Computer aided dispatch. Essentially all trains are monitored via control centers owned by a few of the larger railroads. Passenger traffic is even handed off through these centers when crossing the territories.

And yes dark territory is what they call the areas that are unmonitored. Usually these are way out in the middle of no where on single track. Most monitoring believe it or not is hard wired and not wireless. For example, hot box detectors which are basically buried on the inside of the tracks monitor a trains bearing/axel temperatures and can report if one is over heating. This is critical because it is a source of derailments. Those boxes though usually are wired directly to lines running along the track and back to a common point. In many cases a number of lines terminate at one location and are fed to radio towers that beam that data back. In other cases it follows the fiber all the way to a rail yard or dispatch center.

I can't say now what the differences are with PTC in Europe, but I know when I was at GE we looked a lot at what they were doing because in most cases they are far more serious about their railroads.