I have heard over and over that signals are being replaced because of the changeover to PTC, but I have never understood why. Do the signals somehow interact with the PTC systeM or is this just some kind of government mandate for standardization? I can understand if some box transmits the aspect to PTC but not how the lights themselves make any difference whatsoever. Can someone enlighten me?
At many locations, the replacement signals can display additional signal indications that were not possible with the previous equipment.
PTC was the major excuse (and a correct One, as the old stuff was not compatible) BUT..... The vast majority of the stuff that has been replaced has been in service for 60 years...some longer. Sadly, parts are hard to come by (and NOT made anymore) and the infrastructure was beginning to show its age..
As I wrote in a article for trains magazine last year (concerning the type SC signals on the CNO&TP)...spare parts were like gold, and it was not unusual for a 60 year old part to be replaced with a new part that was 50 years old!