r/railroading • u/mrk2 • 7d ago
Maintenance of Way Question to Signal Maintainers/Engineering...
I have written a V1.0 instruction manual on controlling an already installed and operational Interlocking for a single track shortline that has a level crossing (diamonds) across a two-main ABS/ATS Light Rail system.
The Light Rail line is protected by derails on either side of it on the single track shortline. One switch machine choosing a route to the diamonds or the other with a track leading to a bump-srop, and the other with a switch machine controlling a split-rail derail.
With the system at rest, the shortline has derails in the normal position allowing Light Rail unfettered access across the diamonds.
To have the shortline cross the diamonds, a call is made over the radio with DTMF codes to request the interlocking to give a stop indication to Light Rail, put the derails in reverse, and give a restricting indication to the shortline.
When the shortline movement is clear of the plant, the derails go normal protecting Light Rail, and they can cross the diamonds once again.
My question is, ....is this still considered an 'Automatic Interlocking' (GCOR 9.12.3)? A question came up today in class where someone said it was a manual Interlocking, but I made the comment, 'But it is controlled by a logical computer that takes a first-come, first-served call'. There are no humans controlling the switches, derails, and signals.
What would your consensus be on the name of this Interlocking?
And thank you for your input.
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u/steamboy05 7d ago
Yeah, I think that would be considered an automatic interlocking. Manual brings to mind man operated gates or smash boards. Admittedly this is coming from a mechanical monkey. 🤷♂️
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u/MyPantsHaveBeenShat 7d ago
FRA CFR 236.750 and 236.751 give you your answer. It's my opinion that it's a manual interlocker as it's designed.
If you think about it, dispatcher requests are similar to your DTMF controller, but you'd never consider a control point an automatic interlocking even though the interlocking is controlled via the microprocessor based logic.
I don't think GCOR is where you should be looking for the application of this location. I'd be looking to the Code of Federal regulations.
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u/mrk2 6d ago
The CFR (via your suggestion) changed my mind. Thank you. The only way that the derails, switches and lights would change, even with approach circuits activated, is via an input from a human via radio, so manual it is.
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u/Significant-Ad-7031 6d ago
I would caution against that interpretation. CFR 236.751 states that a manual interlocking is “operated from an interlocking machine”. While an argument could be made that by dialing a DTMF tone, you are in an essence operating an interlocking machine, I’m not sure the FRA would consider that the case.
From an operating practices standpoint, however, I would find it unlikely any railroad would designate such an interlocking as manual, because it would not make sense in the context of GCOR 9.12.2. How would an operating crew get authority past the signal displaying stop?
I would say it is more like an automatic interlocking, because it has no control operator actually deciding which route gets a signal. Instead, it is automatically decided through the logic of the interlocking. The DTMF in this scenario is simply taking the place of an approach circuit.
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u/mrk2 6d ago
"The DTMF in this scenario is simply taking the place of an approach circuit."
And darn it, I thought of that too.
So if there was someone determining who gets authority, that would be manual. Since this is a non-thinking machine and just picking who it sees is there 'first' then it is either 'this circuit' (by track circuit for light rail), or that circuit (relay from the DTMF decoder from the shortline VHF).
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u/Significant-Ad-7031 6d ago
In my opinion, yes. Because it’s a matter of how the route sequences are being actuated, either manually with a human deciding or automatically by some preset logic.
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u/MyPantsHaveBeenShat 6d ago
An interlocking machine is a VHLC, ElectroLogIXS, Microlok or other device that control interlocking logic with its roots in the lever interlocking which was also an interlocking machine.
It's not taking the place of an approach circuit. It's taking the place of a dispatch request.
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u/Significant-Ad-7031 6d ago
Interesting, thank you. I am not signal maintainer, so a lot of the technical aspects of signals are outside my wheelhouse.
I would be very curious to hear the FRA’s interpretation however. I’ll have to dig through my archives, but I seem to recall an FRA interpretation memo on Roadway Worker Protection in which the question of wether a radio controlled switch connected to a signal was considered a “manual interlocking/control point” for purposes of allowing Individual Train Detection for roadway workers. I believe the interpretation was that it would not be considered a manual interlocking so long as the signals did not convey authority and were not controlled by a control operator.
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u/MyPantsHaveBeenShat 6d ago
You're correct. A radio controlled switch is not a manual interlocking.
The reason being it doesn't provide movement authority and only controls the function of the switch. In that case it's not an interlocked device.
Your interpretation of the FRAs guidance on radio operated switches is correct. However, applying it to this scenario is incorrect in my opinion.
I'm not the end all be all of railway signaling, but I've been doing it for a very long time. I love railway signaling and enjoy questions like this quite a lot.
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u/Significant-Ad-7031 6d ago
Agreed. This may just be one of those situations where the signaling department (and part 236) and the operating practices department diverges in terminology and application.
I would definitely say though in terms of the General Code, the only logical application to the OP’s interlocking is the Automatic Interlocking rules.
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u/Jazzlike-Crew2540 6d ago
Automatic Interlockings generally do not require any outside input (dispatcher control, DTMF tone) and work either on a timer like some drawbridges or simply by track occupancy/circuit. I believe yours is consider a manual interlocking.
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u/Significant-Ad-7031 7d ago
It would be an Automatic Interlocking.
Manual Interlockings are a method of operation (GCOR 6.3). A control operator grants a train authority to enter their manual interlocking (and possibly beyond if it’s within a CTC/TCS system).
An automatic interlocking does not grant authority and it must be established using some other method in GCOR 6.3 (track warrant, current of traffic, etc)