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New Signals & Interlockings Book

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  • Member since
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Posted by 7j43k on Wednesday, April 28, 2021 11:32 PM

ATLANTIC CENTRAL

 

Interlockings really are the heart of how trains are controlled on the big railroads.

And, just my opinion, it is the only part of signaling we really need on our model layouts.

We don't have long runs of track thru the country side where multiple trains will follow each other for dozens or even 100 miles.

We are lucky if we have a scale mile between logical junctions/interlockings/control points. 

 

 

By that reasoning, the "railroad" will be a collection of interconnected interlockings, with negligible connecting trackage.

So a train leaves terminal A, and has a pre-determined route through the appropriate interlockings, until it reaches terminal B.  Since each interlocking will not allow opposing movements, all opposing trains will be stopped by red signals.  Once the train is through the collection of interlockings, another train may be run through the collection. 

In a sense, it's like one BIG interlocking, allowing only one train through at a time.

You CAN run multiple trains through this system at the same time IF you can guarantee each route is separate from all the others.

What you cannot do is guarantee that each train will be protected by a red signal at each end of its block--ABS.  Interlockings don't indicate occupancy; they indicate permission.

So only one train can occupy any route at any particular time.  You can't send out a following train until the previous one has arrived.

 

Ed

  • Member since
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  • From: Maryland
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Posted by ATLANTIC CENTRAL on Thursday, April 29, 2021 5:49 AM

7j43k

 

 
ATLANTIC CENTRAL

 

Interlockings really are the heart of how trains are controlled on the big railroads.

And, just my opinion, it is the only part of signaling we really need on our model layouts.

We don't have long runs of track thru the country side where multiple trains will follow each other for dozens or even 100 miles.

We are lucky if we have a scale mile between logical junctions/interlockings/control points. 

 

 

 

 

By that reasoning, the "railroad" will be a collection of interconnected interlockings, with negligible connecting trackage.

So a train leaves terminal A, and has a pre-determined route through the appropriate interlockings, until it reaches terminal B.  Since each interlocking will not allow opposing movements, all opposing trains will be stopped by red signals.  Once the train is through the collection of interlockings, another train may be run through the collection. 

In a sense, it's like one BIG interlocking, allowing only one train through at a time.

You CAN run multiple trains through this system at the same time IF you can guarantee each route is separate from all the others.

What you cannot do is guarantee that each train will be protected by a red signal at each end of its block--ABS.  Interlockings don't indicate occupancy; they indicate permission.

So only one train can occupy any route at any particular time.  You can't send out a following train until the previous one has arrived.

 

Ed

 

Interlocking signals do indicate both permission and occupancy. Dispatchers can give your clear indications all day long, but if another train is still in the block, or a non CTC turnout is set wrong, your signal will stay red.

If your layout is big enough and your trains short enough, sure you can make the whole thing work like the prototype.

Single track or double track makes a big difference too.

Out of time now, more later.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Thursday, April 29, 2021 6:23 AM

Ok, I have a other minute or two.

Yes, where distances are great, ABS can protect long stretches of track with automatic control point passing sidings with bidirectional traffic in both directions between CTC interlockings on single track.

Show me a layout where you can really model that with 35 car trains?

Sheldon

 

    

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Posted by 7j43k on Thursday, April 29, 2021 9:39 AM

ATLANTIC CENTRAL

Interlocking signals do indicate both permission and occupancy.

 

No.  Not occupancy.  Not for the interlocking, and not for anything a train encounters after the interlocking.  That is all ABS.

Note that the indications projecting outwards from the interlocking don't change from just before a train enters, and after it HAS entered.  Hence, no occupancy.

Dispatchers can give your clear indications all day long,...

The only way dispatchers can give you clear indications is with a CTC panel, and that ALWAYS includes ABS.

but if another train is still in the block, or a non CTC turnout is set wrong, your signal will stay red.

If you are talking about an interlocking, as you say you are, then yes, you get a red if your route is not cleared.  And until the tower operator aligns your route, it will stay red whether or not "another train is still in the block".  It will only change for YOU if the tower operator resets the interlocking.

You can point out, reasonably, that the tower operator can examine his interlocking and HE is the occupancy detector.  But note that he is NOT the occupancy detector for the trackage AFTER the interlocking.  So, without ABS, he can direct your exiting train right into another train that he has holding for a red until you clear.  

To deal with THAT, you have to have him also responsible for tracking trains outside his interlocking, which isn't his job.

 

Ed

 

 

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Posted by 7j43k on Thursday, April 29, 2021 9:53 AM

ATLANTIC CENTRAL

Ok, I have a other minute or two.

Yes, where distances are great, ABS can protect long stretches of track with automatic control point passing sidings with bidirectional traffic in both directions between CTC interlockings on single track.

Show me a layout where you can really model that with 35 car trains?

Sheldon

 

 

ABS does protect long stretches of track.  It also protects interlockings that don't have long stretches of track between them.  When ABS is present, it is also applied to interlockings.

You don't need to run 35 car trains to have and use ABS.

If you want signaled interlockings but do not want ABS, you will be operating with timetables and train orders.  For a model train layout, that is typically done by asking "someone" if it's OK to go on this track to the next town or whatever.  I suppose you can give this job to your towermen.

 

Ed

 

 

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Posted by ATLANTIC CENTRAL on Thursday, April 29, 2021 10:29 AM

7j43k

 

 
ATLANTIC CENTRAL

Ok, I have a other minute or two.

Yes, where distances are great, ABS can protect long stretches of track with automatic control point passing sidings with bidirectional traffic in both directions between CTC interlockings on single track.

Show me a layout where you can really model that with 35 car trains?

Sheldon

 

 

 

 

ABS does protect long stretches of track.  It also protects interlockings that don't have long stretches of track between them.  When ABS is present, it is also applied to interlockings.

You don't need to run 35 car trains to have and use ABS.

If you want signaled interlockings but do not want ABS, you will be operating with timetables and train orders.  For a model train layout, that is typically done by asking "someone" if it's OK to go on this track to the next town or whatever.  I suppose you can give this job to your towermen.

 

Ed

 

 

 

My system is designed to work as CTC with the dispatcher on duty, and act like timetable and train order with no dispatcher on duty. Operators actually can become their own tower operators. I'm modeling 1954. 

Each interlocking is on the CTC panel, and has its own local tower panel as well.

Further back in this thread is a fairly complete description.

The double track mainline will be signaled for bidirectional traffic.

At no point is there more than two blocks between interlockings, in some cases only one. 

Remember it is DC and the distances and train lengths do not justify any more blocks.

When the the dispatcher sets a route and gives authority, that also connects the correct throttle to the block ahead and provides the correct signal aspects.

Nothing would be gained with an ABS overlay.

Sheldon

    

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  • From: Maryland
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Posted by ATLANTIC CENTRAL on Thursday, April 29, 2021 10:39 AM

Ok, maybe we have a misunderstanding of terms.

I'm only modeling the ABS as it effects the CTC interlockings, with no intermediate blocks, and without any permissive signals.

The fundamental problem with signaling is it is always tailored to the situation, terms and definitions aside.

Sheldon

    

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Posted by 7j43k on Thursday, April 29, 2021 11:25 AM

Sheldon,

You mention having one to two blocks between interlockings.  As you say, those block affect the interlockings.  And the other way.  If one of those blocks has a train in it, signaling should keep the interlocking from showing a green for a following train to also enter that block.

And since there are so few blocks between interlockings, it does look like you'll have an ABS system overlaid onto your interlockings.

I've had a quick look at your track plan, and I do see sections of track between interlockings that I would detect.  For a single block, the signals themselves would surely be a part of the adjacent interlocking signals.

For that one two-block section, it looks like you'll need a single pair of stand-alone ABS signals.  Which, I agree, is pretty close to zero.

I also get your point about layouts being so compact that they don't need very many signals between interlockings.  Around here, where all Free-mo modules are expected to be MSS (ABS) equipped, there's been talk of having signals too close together to be believable.

For my signaled module, I've set it up so I can insert either a working signal pair, or an abandoned location.

 

Ed

Ed

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  • From: Maryland
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Posted by ATLANTIC CENTRAL on Thursday, April 29, 2021 11:34 AM

Ed, now you have it, and yes it is simplified from the prototype.

And yes it has always been my understanding of the prototype that an interlocking signal will not clear if there is a train in the block ahead if ABS is imbeded over the the interlocking CTC.

And understand, this is based on my understanding of a number of systems from my era and region.

The primary reason there is even two blocks between some interlockings is to allow switching to happen at both ends at the same time.

Cabs are assigned to throttles by pushbuttons that are duplicated at the tower panels at each end of the block and on the CTC panel. Route, cab assignment (permission) and occupancy control the signals.

And the system also has ATC (automatic train control), if you run a red signal, your train just stops.

Sheldon

    

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Posted by ROCK MILW on Thursday, April 29, 2021 4:00 PM

According to my GRS book "Elements of Railway Signaling', an interlocking signal can be cleared to yellow if the block ahead is occupied and the stick relay is up (i.e., the traffic entering the interlocking is following traffic moving the same direction.) This is shown in Figure 924 by relays 45S (stick) and 45YGP. The latter relay would be down in this condition, where APB is operative:

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Posted by ATLANTIC CENTRAL on Friday, April 30, 2021 4:46 PM

I received my copy today. After a quick scan, I will say nicely done for such a complex suject in only 141 pages.

Even before an in depth read, I feel it was a worth while addition to the library that will prove useful.

I found the opening line of Chapter 6 interesting "The heart and soul of mainline railroading is the interlocking" - seems I said something similar earlier in this thread.......

I have seen articles about building working interlocking machines before, also an interesting concept.

My take on that is this - I have my turnouts controlled by pushbuttons that in many cases select a whole route, rather than just operating one turnout.

The wiring schemes I do this with involve some simple relay logic, and interestingly provide route interlocking just like a mechanical machine. 

Conflicting routes cannot be selected and signals will only display the selected route. 

More later,

Sheldon

    

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