What ever happened to ATS in Southern California? ATSF used to have ATS in place on the 4th and 2nd subs. From what I have been able to read, that is what PTC is tantamount to. I also have read nothing since the Chatsworth tragedy about the eyewitness accounts of observing a green aspect on the signal controlling the siding there. Being a technical person, I would offer the suggestion that a system using IP technology be used to control the signals, and retrofit the signals to use a fiber optic sampler of the optical output of the signals and use a return link to give the dispatcher assurance that the correct aspect has been displayed. This would not require a large dollar figure per signal to implement. A dedicated wired or wireless domain could isolate it from Internet failures as well. Any conflict between the command for a signal and the returned aspect data would implement the same response as a blown signal by a train: immediate maximum brake application. This could be implemented as an extra layer to the proposed PTC.