signal timing

how long before the train comes does a signal light up and appear? I'm sure there are many different variables, such as; (I'd assume) whether it's CTC or ABS, or the number of tracks, and the line etc. But does anyone have a general kind of description to the answer?
Any information is appreciated.


thanks

Many, many variables. On sections where the signals are lit continuously, the clear signal will come up as soon as the dispatcher lines up the circuits. On lines where the signal only lights up when there's equipment shunting the circuit, the signal will show an indication, any indication, only when the track is shunted in either direction ahead of the signal.

There are other variables. On parts of the old Nickel Plate (I had noticed this as a kid when I walked to school along the right-of-way) an indication other than clear would light the signal up, shunt or no shunt. So, a train clearing a block would show red, then approach, and then darken.

So, you see? It depends on the signal system and the setup.

On the Oregon Trunk sub (ex SP&S) 90% of the signals are the original searchlight type that were installed with the ABS. Most of them are clear 24 hours a day, then change accordingly when a train comes or goes. However a few ''going up the hill'' dont display an aspect until shunted which was for some reason was when we were about 2500 ft from the signal. We told the signal dept. about this and I never did find out if it was a malfunction or not. The whole system is the old 6 volt system. From what I hear one of the last on the BNSF.

On the ex-B&O near my Baltimore home, there is a signal bridge which controls an interlocking (so always lit, absolute stop most of the time) and there is an old B&O style CPL which is only lit when a train is in the block. This is excellent for a southbound train since it will enter the block 10-15 minutes before passing the signal, but horrible for a northbound train, since the block appears to begin near the howard st tunnel, so the only warning you have is the increasing odor of deisel.

Depends on the signal system practice of the particular line.

On the CSX Chicago Line here in western NY, signals light only when there’s a train in the block in advance of the signal. This holds true for both absolute (controlled) signals and automatic block signals.

However while the signals may be dark, searchlight signal heads' internal mechanisms still operate continuously to display whatever aspect is commanded by the signal system.

This can be seen by observing an unlit west-facing signal with the setting sun shining into it, or by aiming a bright flashlight into an unlit signal after dark. Even though the signal lamp is off, depending what the system is commanding you can observe a red, yellow or green “phantom" (reflected) aspect . Thus you can often determine how a route is lined, or determine occupancy of up to two blocks beyond the signal even though the signal itself is not illuminated.

Also - the CSX Chicago Line is double tracked and signalled for operation in both directions on both tracks. Signals are arranged so the signals for BOTH tracks always light up even though only one track's approach block may be occupied. (Maybe a safety feature so train crews can observe/report signal malfunctions on the adjacent track? - I don't know...)

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The defunct Lehigh Valley used a slightly different signal lighting arrangement – at least for a couple block signals and an interlocking I could observe near home.

LV absolute signals were continuously lit. Most of the time they displayed red over red (stop). They’d only change to green over red (clear block) perhaps 10 – 15 minutes before a train would show up.

Automatic block signals however were normally dark. They would light either when the block in advance of the signal was occupied OR whenever an indication less favorable than clear was being given by the signal. Thus the normal display sequence for a train passing an automatic was:

(DARK) - system at rest (the signal mechanism however would display green if had been lit or you were to shine a flashlight at it)
GREEN – signal lights up the instant the locomotive enters the block in advance of this signal (ie. passes the next signal in advance).
RED – as the locomotive passes this signal.
YELLOW – after the last car has passed the NEXT signal beyond.
(DARK) – after the last car has passed the SECOND signal beyond. (Mechanism however is now again set to display green)

In the final few years of LV operation the automatic signals near us were changed to continuously lit operation. (Perhaps to eliminate maintenance on approach lighting circuits? I don’t know…) However even after the LV ceased operations the signals near us remained lit for several months afterward until they were taken down or shot out.

Approach lit signals are controlled by block occupancy so the "how long?" time factor depends on the speed of the train and the length of the block.

thanks

FarmallBob:

Lehigh Valley Railroad absolute signals, main track, Niagara Jct- Blacksmith were controlled by the operator at Niagara Jct. under authority of the Buffalo Division dispatcher. When the dispatcher would give the authority, the operator would set the signal for the route called for. Spent a fair amount of time at the Niagara Jct. tower 1973-1976. Sometimes the dispatcher would give the authority an hour ahead of the movement and at other times 10 to 15 minutes as you mentioned.