Can anyone tell me what type of signal Southern Pacific would have used where the X is in the following track arrangement?
/------------------------------\ --------------------------------------------- X \------------------------------/
The era is mid 1970’s using searchlight signals. Since SP used route signalling It seems to me they would have placed a triple head signal there. But others I’ve talked to tell me they would have used a double head to indicate either clear or diverging. There would be no room for multiple masts.
Assuming its CTC, there would most likely be one mast with two heads. Diverging is diverging, it doesn’t matter which siding the train is lined towards, its the same signal indication.
Assuming its ABS, it could even be a single head, since there would be no diverging signal.
Perhaps it depends on the location, the portions of the SP with which I’m familiar do not seem to have been route signaling, but that’s a while ago and I may remember incorrectly. What is the location and situation? Centralized Traffic Control or Automatic Block Signaling?
Thanks, It is CTC. I also have a 1976 Rulebook. Where I am unclear on is the use of a double head vs. a triple head signal. If the example in my first post would use a double head signal, when would a triple head be used (excluding the lower head being a lunar). Would it be the case of a siding or track off of a siding?
/------------------\ /------------------------------\ ---------------------------------------------------- X
I think in your original example, the two headed signal would be enough. The crew’s orders would specify which track they would to into, like “take north siding to meet train 123”.
If CTC and both sidings are signaled and both are the same speed a two headed signal would do.
If CTC and both sidings are signaled but are different speeds, with routing signaling a three headed would be used and a special instruction would need to be issued to inform crews which of the two lower heads is for which switch.
If CTC on main track but sidings unsignaled a two headed signal with bottom showing restricting when lined for siding.
If ABS and hand throw switches a one headed signal with a switch indicator light to tell crews to stop and open switch to take siding. Crews would have to ascertain which siding unless special instructions in place.
If ABS and hand throw switches and siding designated by direction, no signal necessary.
Not quite. A three headed signal could be used or just a two headed signal could be used. The crews just follow the signal indication, there is no need for a special instruction. Signal heads do not apply to individual tracks. There are no diverging alternate signals you could use for different tracks anyway.
I agree.
The 1976 SP rules do not have a provision for a “switch indicator” (which is more properly a take siding indicator). The instructions to take siding would be conveyed in the train orders or DTC authorities granted.
In my experience there would be a single headed signal.
"…If CTC and both sidings are signaled but are different speeds, with routing signaling a three headed would be used and a special instruction would need to be issued to inform crews which of the two lower heads is for which switch.
Not quite. A three headed signal could be used or just a two headed signal could be used. The crews just follow the signal indication, there is no need for a special instruction. Signal heads do not apply to individual tracks. There are no diverging alternate signals you could use for different tracks anyway. "
This is kind of a yes and no point. It would depend on how busy the area is and/or how quick the SP wants the trains in the clear. If one switch is say 10mph and the other is 30mph each train would have to slow prepared to head in at 10mph until they had ascertained which siding they were going into. Reason is on a diverging indication on a two headed signal is the same for either route. If the SP desires not to slow trains down unecessarily and/or get them in the clear quickly on the faster track they could add another head to the signal mast a say in a S.I. that the middle head is for the 30mph switch and the bottom head governs the 10mph switch. Over the years I’ve seen many situations like this on several roads. It all boils down to what the SP wants to accomplish and how quickly. That was my reasoning for a three headed signal, if the railroad doesn’t care and just wants the cheap fix a two headed is all they need.