| Posted by mmi16 on August 20, 2025 | |
B&O/CSX have signals that are both approach lit as well as constant lit. In more recent years with the installation of the so called Darth Vader signals that replaced the B&O CPL's everything is approach lit.
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On former PRR and UP, for instance, signals in CTC territory were clear in one direction and stop in the other according to prevailing current of traffic on a particular track. B&O's here and on some other roads' systems, the indications remained clear in both directions when no movement was establishing a current of traffic. Santa Fe had constantly lit signals on many lines dating to double track or single track ABS territory times, but the point here is these signals, on the Magnolia Cut-off in this case, remained a neutral clear in both directions on the same track when the system was "at rest" and, as such, could also portend of approaching traffic when activated. The legacy signal systems were fascinating appurtenances quite unique to each carrier in many cases.
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| Posted by mmi16 on August 22, 2025 | |
The thing to remember about Intermediate Signals - they indicate occupancy of the blocks ahead of their location. In the 'normal' Clear, Approach, Stop progression of signals - if two or more signal blocks ahead of the signal you are looking at have no trains occupying them - the signals (if constant lit) will indicate Clear in either and/or both directions. If the Intermediate is followed by a controlled signal, and that signal is set at STOP, the Intermediate leading to it will indicate Approach.
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Yes, that's all well and good but missing the point that I am making about signals remaining clear (or approach) in both directions on the same track when the system is "at rest" (nothing lined into or occupying the block) that was not a universal arrangement. This was more often a single track ABS procedure. Best regards.
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| Posted by mmi16 on August 22, 2025 | |
Constant Lit - no occupancy of two signal blocks ahead of the signal(s) you are looking at which displays CLEAR. Since tracks are signaled in both directions, the other side of the signal with no occupancy for two signal blocks - that signal displays CLEAR.
O========O========O=========O=========O
Stop Approach Clear Approach Stop
At the time of your photo signal blocks were nominally two miles long. With the upgrades made necessary by the implementation of PTC the nominal length of signal blocks are now about three miles long.
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Sure, clear precedes approach and so forth; elementary my dear Watson. Again, the point is that this signal system shows a favorable indication in both directions on unoccupied CTC track - that is unique to some roads as opposed to lines such as PRR, UP and others that only display a favorable indication in the direction currently or last established. PRR even had traffic levers to establish current of traffic on tracks signaled in both directions (Rule 261). The overall point I was trying to make is the differences in signal systems of the various predecessor roads (like C&Os exit signals at control points or "cabins" in their vernacular), that have since largely become a generic sameness.
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| Posted by mmi16 on August 24, 2025 | |
Automatic Block Signals display the condition of the signal block(s) in the advance of the signal location - in ALL directions. When no 'traffic direction' has been established on a track segment between Control Points (the only place Absolute Signals exist) the Intermediates will display the most permissive indication possible. The lining of a Control Point signal into a track segment will establish the traffic direction on that track segment at the time the signal gets lined.
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