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First, one of the goals of PTC is to be able to extend signal-type protection to non-signaled track. If you have to install a signal system (circuits in the track) then you eliminate part of the benefit. Second, the crew doesn't know when they will be taking a siding or necessarily why. That is controlled by the dispatcher. Third, the train length is provided by the lists and is fairly accurate, depending on wether the train has picked up or set out cars enroute. Fourth, yes but what happens to the trains behind the train when it loses contact? If the train ahead disappears does the system let the following train speed up? If an opposing train disappears, does the system let the train in the siding out on the main? You have to account for loss of contact because it will happen. Fifth, yes but you would have to install it in every engine and every EOT, and it would have to be interactive, transmitting a location as well as recieving it. That's a couple hundred thousand things to keep track of. Throw in on track vehicles and maintenance equipment, there's another hundred thousand things to track. That's a lot of satellite air time. Sixth, that info is nice to know, but really the only thing they need to know is what signal indication or speed they need to move on or how long they will be stopped (to cut crossings, etc). Seventh, you would probably need CTC to remain in effect at all times as a back up. Remember your first point, those signals in the track? Well that is a more complicated CTC system, so you can say you are "retiring" it but in reality you aren't, you still have all and more of the cost with your coded signals in the track. Finally because a little map isn't interactive. You don't have to be two way with a handheld mapper, you don't have to have it stand up in -50 deg with a 90 mph wind and 2 ft of snow and then 120 deg heat a month later. Your littel GPS indicator doesn't have to be 99.99999% reliable. Why do you think you can buy a am-fm radio for $10 but it costs thousands, if not hundreds of thousands for a commercial grade airline communications system. You won't run this off of a PC either. The amount of data you will have to process on a real time basis to track 10 or 20 thousand elements moving across a grid of several hundred million points is staggering. This would have to be a multi main frame based system. It becomes a big deal real fast. Smith
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