CTC Overview

High level design overview for CTC signalling (from discussions with Gene on Oct 14, 2006):
1.) Line-side wiring consists of Upper Crossarm = signal to signal local control and Lower Crossarm = AC Power + 2 wire CTC data line.
2.) Modern version of above is power to each CTC control point (CP) with local power, send CTC data to each CP from dispatcher location, and signal to signal local control via Electricode or equivalent (signals travel on rails).
3.) CTC dispatcher link for 2. above is currently via 900mhz radio for UP and Fiber for BNSF.
4.) CTC Control Point (CP) is located at every siding switch. Intermediate block signals are local control only between CPs.
5.) Local control is primary (for safety) and CTC just sends a desired command but that command will not take effect if local control determines it is unsafe.
6.) Early CTC sent commands and received responses but had no dispatcher side logic to determine if it was safe -- if an unsafe condition was sent, the dispatcher would just see that it was ignored and would need to determine what he had missed.
7.) Later CTC had dispatcher side logic that mimiced the field track signal logic and would inform dispatcher of conflicts during setup and prior to sending it to the railside signals.