Auto Reverse Segments in DCC


mgj21932
 

I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?  

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

 

Thanks in advance.  

Bill D
N&W Steam Only


whmvd
 

Bill,

I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?

In practice, you will probably get away with longer trains with just metal wheels not connected electrically to other axles at least 99% of the time. In the remaining <1%, there may be a short reported - or not if you're lucky. If not, you won't even notice anything amiss at all. But it's still not a good idea. If you add in the system that some people use to stagger the gap between left and right rail (which I am 100% sure is pointless, but does no harm normally) then the 99% will drop significantly, in line with the length of the staggered bit.

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

That is certainly safe. Even one loco OF a powered consist is plenty. Shorter will work, but there is no set shortest distance. Stick to the length of your shortest loco and you'll be good (although if you push a train instead of pull things need to be looked into more carefully).

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

Q1 is about how one autoreverser works, whereas Q2 is about preventing two AR sections  from in-fighting. It's like asking for the difference between inflation and the exchange ratio between dollar and euro. They are both about money, but there is no other relation.

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

That is correct. It's all about not crossing both gaps simultaneously.

Wouter

 

Thanks in advance.  

Bill D
N&W Steam Only


D B
 

Wouter, 
Thanks for the authoritative answers.  The minimum length issue is really critical to the design and operation of my layout.  My minimum length concern arose when I realized the N&W passenger train, pulled by a J, that I had painstakingly assembled and planned to be a signature hallmark of the layout was longer than one of my two AR segments. That appeared to require a fundamental reworking of my track plan.   However, the redesign would have imposed significant limitations on operations.  I believe I’ll accept the <1% risk in order to improve operational flexibility (including the realistic opportunity to run two trains simultaneously).
Your advice is greatly appreciated. 
Bill D
N&W Steam Only


On Nov 5, 2021, at 5:11 PM, whmvd <vandoornw@...> wrote:


Bill,

I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?

In practice, you will probably get away with longer trains with just metal wheels not connected electrically to other axles at least 99% of the time. In the remaining <1%, there may be a short reported - or not if you're lucky. If not, you won't even notice anything amiss at all. But it's still not a good idea. If you add in the system that some people use to stagger the gap between left and right rail (which I am 100% sure is pointless, but does no harm normally) then the 99% will drop significantly, in line with the length of the staggered bit.

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

That is certainly safe. Even one loco OF a powered consist is plenty. Shorter will work, but there is no set shortest distance. Stick to the length of your shortest loco and you'll be good (although if you push a train instead of pull things need to be looked into more carefully).

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

Q1 is about how one autoreverser works, whereas Q2 is about preventing two AR sections  from in-fighting. It's like asking for the difference between inflation and the exchange ratio between dollar and euro. They are both about money, but there is no other relation.

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

That is correct. It's all about not crossing both gaps simultaneously.

Wouter

 

Thanks in advance.  

Bill D
N&W Steam Only


Blair
 

Well, if it's one train, perhaps consider plastic wheel sets on the last two or three cars, if you have problems? Just a thought.

On 2021-11-05 23:31, D B wrote:
Wouter, 
Thanks for the authoritative answers.  The minimum length issue is really critical to the design and operation of my layout.  My minimum length concern arose when I realized the N&W passenger train, pulled by a J, that I had painstakingly assembled and planned to be a signature hallmark of the layout was longer than one of my two AR segments. That appeared to require a fundamental reworking of my track plan.   However, the redesign would have imposed significant limitations on operations.  I believe I’ll accept the <1% risk in order to improve operational flexibility (including the realistic opportunity to run two trains simultaneously).
Your advice is greatly appreciated. 
Bill D
N&W Steam Only


On Nov 5, 2021, at 5:11 PM, whmvd <vandoornw@...> wrote:


Bill,

I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?

In practice, you will probably get away with longer trains with just metal wheels not connected electrically to other axles at least 99% of the time. In the remaining <1%, there may be a short reported - or not if you're lucky. If not, you won't even notice anything amiss at all. But it's still not a good idea. If you add in the system that some people use to stagger the gap between left and right rail (which I am 100% sure is pointless, but does no harm normally) then the 99% will drop significantly, in line with the length of the staggered bit.

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

That is certainly safe. Even one loco OF a powered consist is plenty. Shorter will work, but there is no set shortest distance. Stick to the length of your shortest loco and you'll be good (although if you push a train instead of pull things need to be looked into more carefully).

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

Q1 is about how one autoreverser works, whereas Q2 is about preventing two AR sections  from in-fighting. It's like asking for the difference between inflation and the exchange ratio between dollar and euro. They are both about money, but there is no other relation.

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

That is correct. It's all about not crossing both gaps simultaneously.

Wouter

 

Thanks in advance.  

Bill D
N&W Steam Only


Dale Gloer
 

Bill,

depending on which devices you are using for autoreversing, you may be able to connect two autoreversing sections back to back without an intervening non-reversing section.  I know for sure of one such device - it is the DCC Specialties PSX-AR available from Tony's Train Exchange.  The PSX-AR has an option to be set as a Slave autoreverser which allows it to be connected directly to another PSX-AR that is the Master.  This works very well as our club layout has two such combinations.  I do not know of others though.

I have no affiliation with Tony's or DCC Specialties - just a satisfied user.

Dale Gloer


Don Vollrath
 

The minimum length of fixed polarity track between two AR sections needs to be only as long as a typical power pickup truck where more than one axle and steel wheels are connected electricity together. (Think diesel truck or steam engine drivers)
Then as that truck spans the gap from the “leaving” AR #1 and enters fixed polarity track it will cause AR-1 to flip to agree with the fixed polarity.
Then as that same truck spans the gap at the other end of the fixed polarity section into AR-2, AR-2 will also be caused to flip to match the fixed polarity. So then AR-1 = fixed = AR-2. DONE

So how long does the fixed polarity track section need to be ? Only as long as the multi-axle power pickup truck. Any additional length is unnecessary.

DonV


D B
 

Wow, Dale, thanks for that information.  I believe that is new to the previous discussion of this topic some months ago.  Great addition to our collective knowledge base. 
Bill D
N&W Steam Only


On Nov 6, 2021, at 10:54 AM, Dale Gloer <dale.gloer@...> wrote:

Bill,

depending on which devices you are using for autoreversing, you may be able to connect two autoreversing sections back to back without an intervening non-reversing section.  I know for sure of one such device - it is the DCC Specialties PSX-AR available from Tony's Train Exchange.  The PSX-AR has an option to be set as a Slave autoreverser which allows it to be connected directly to another PSX-AR that is the Master.  This works very well as our club layout has two such combinations.  I do not know of others though.

I have no affiliation with Tony's or DCC Specialties - just a satisfied user.

Dale Gloer


D B
 

Thanks Don. That confirms my understanding too. And an excellent explanation as well.
I plan a segment as long as my N&W A loco and tender to be safe, but that’s not all that long and there’s no intervening track turnouts or other issues which would require a shorter non-reversing segment.
Bill D
N&W Steam Only

On Nov 6, 2021, at 10:57 AM, Don Vollrath <donevol43@hotmail.com> wrote:

The minimum length of fixed polarity track between two AR sections needs to be only as long as a typical power pickup truck where more than one axle and steel wheels are connected electricity together. (Think diesel truck or steam engine drivers)
Then as that truck spans the gap from the “leaving” AR #1 and enters fixed polarity track it will cause AR-1 to flip to agree with the fixed polarity.
Then as that same truck spans the gap at the other end of the fixed polarity section into AR-2, AR-2 will also be caused to flip to match the fixed polarity. So then AR-1 = fixed = AR-2. DONE

So how long does the fixed polarity track section need to be ? Only as long as the multi-axle power pickup truck. Any additional length is unnecessary.

DonV




jfm2830
 

In regards to your question #1.  You need to understand how a reversing section works.  When a car with metal wheels crosses the gap at the beginning of the reversing section, the metal wheels cause a momentary short across the gap which the AR senses and flips polarity to correct.  The train then progresses thru the reversing section with no further shorts until the lead car or engine's metal wheels cross the exit gap.  Then there is a momentary short across the gap which the AR senses and flips polarity to correct just like when the train was entering the reversing section.  Now if the entire train is in the reversing section everything it great.  However, if the train is longer then the reversing section, then as a car towards the rear of the train enters the reversing section, there is a short again and the reversing section flips.  Then a car leaving the section crosses the gap, another flip gets triggered and the reversing section keeps flipping back and forth as cars enter or leave the section.  Not a problem unless both entrance and exit gaps get shorted at the same time, then you have a problem.  If it is only cars crossing both gaps this it not likely unless the distance between the exit and entrance gaps is an exact multiple of the car length.  However, if a loco is crossing one of the gaps, it shorts the gap the entire time it is entering or leaving (front and rear trucks are connected) and then you have a problem if a car is entering the section at that time.  If the cars have plastic wheels then this is not an issue.
Good Luck, John Moonan


D B
 

Thanks John.
I do understand and agree with your explanation. Sounds like that is the basis for Wouter’s "99% of the time" assessment.
Query, in your view (and for purposes of Wouter’s 99% assessment), does it matter whether the cars (passenger) are lit?
Bill D
N&W Steam Only


whmvd
 

It matters very much. Fatally, for too long trains. Nobody would feed the interior lights off just one axle, and as soon as you have more than one the die is cast.

Wouter

On Sat, 6 Nov 2021, 19:17 D B, <1932mgj2@...> wrote:
Thanks John. 
I do understand and agree with your explanation.  Sounds like that is the basis for Wouter’s "99% of the time" assessment. 
Query, in your view (and for purposes of Wouter’s 99% assessment), does it matter whether the cars (passenger) are lit?
Bill D
N&W Steam Only





D B
 

Thanks Wouter.  That’s what I feared. 
 
My original question, to which you posted a most helpful response (and on which your 99% assessment likely was predicated), assumed no lights in trailing cars.  

Your definitive response to the change in assumptions is most helpful in my track planning.  I’ll follow the standard practice of making the AR segment longer than longest (lighted) passenger train. 

Bill D
N&W Steam Only


On Nov 6, 2021, at 9:08 PM, whmvd <vandoornw@...> wrote:


It matters very much. Fatally, for too long trains. Nobody would feed the interior lights off just one axle, and as soon as you have more than one the die is cast.

Wouter

On Sat, 6 Nov 2021, 19:17 D B, <1932mgj2@...> wrote:
Thanks John. 
I do understand and agree with your explanation.  Sounds like that is the basis for Wouter’s "99% of the time" assessment. 
Query, in your view (and for purposes of Wouter’s 99% assessment), does it matter whether the cars (passenger) are lit?
Bill D
N&W Steam Only





D B
 

Given this limitation, my lengthened AR segment will now include a turn out.  I assume that, properly insulated, the only operational limitation the presence of the turn out presents is to avoid having a train cross the “AR gap” at the turnout while another train is crossing the AR gap at one or the other of the two “ends” of the AR segment.  
Bill D
N&W Steam Only


On Nov 6, 2021, at 9:08 PM, whmvd <vandoornw@...> wrote:


It matters very much. Fatally, for too long trains. Nobody would feed the interior lights off just one axle, and as soon as you have more than one the die is cast.

Wouter

On Sat, 6 Nov 2021, 19:17 D B, <1932mgj2@...> wrote:
Thanks John. 
I do understand and agree with your explanation.  Sounds like that is the basis for Wouter’s "99% of the time" assessment. 
Query, in your view (and for purposes of Wouter’s 99% assessment), does it matter whether the cars (passenger) are lit?
Bill D
N&W Steam Only





Blair
 

Bill

Sounds like you've discounted this option.  Keep it in mind, though, as should your desired train length increase, you'll otherwise run afoul of the AR length again.

Blair

On 2021-11-06 7:55, Blair wrote:

Well, if it's one train, perhaps consider plastic wheel sets on the last two or three cars, if you have problems? Just a thought.

On 2021-11-05 23:31, D B wrote:
Wouter, 
Thanks for the authoritative answers.  The minimum length issue is really critical to the design and operation of my layout.  My minimum length concern arose when I realized the N&W passenger train, pulled by a J, that I had painstakingly assembled and planned to be a signature hallmark of the layout was longer than one of my two AR segments. That appeared to require a fundamental reworking of my track plan.   However, the redesign would have imposed significant limitations on operations.  I believe I’ll accept the <1% risk in order to improve operational flexibility (including the realistic opportunity to run two trains simultaneously).
Your advice is greatly appreciated. 
Bill D
N&W Steam Only


On Nov 5, 2021, at 5:11 PM, whmvd <vandoornw@...> wrote:


Bill,

I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?

In practice, you will probably get away with longer trains with just metal wheels not connected electrically to other axles at least 99% of the time. In the remaining <1%, there may be a short reported - or not if you're lucky. If not, you won't even notice anything amiss at all. But it's still not a good idea. If you add in the system that some people use to stagger the gap between left and right rail (which I am 100% sure is pointless, but does no harm normally) then the 99% will drop significantly, in line with the length of the staggered bit.

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

That is certainly safe. Even one loco OF a powered consist is plenty. Shorter will work, but there is no set shortest distance. Stick to the length of your shortest loco and you'll be good (although if you push a train instead of pull things need to be looked into more carefully).

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

Q1 is about how one autoreverser works, whereas Q2 is about preventing two AR sections  from in-fighting. It's like asking for the difference between inflation and the exchange ratio between dollar and euro. They are both about money, but there is no other relation.

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

That is correct. It's all about not crossing both gaps simultaneously.

Wouter

 

Thanks in advance.  

Bill D
N&W Steam Only


whmvd
 

Bill,

If you succeed in doing that, you can forget about it and it'll never come back to bite you. If it turns out to be difficult, you can always post the track plan here and ask others for advice. That won't be me, though - not my party trick!

Wouter

On Sun, 7 Nov 2021, 02:12 D B, <1932mgj2@...> wrote:
Thanks Wouter.  That’s what I feared. 
 
My original question, to which you posted a most helpful response (and on which your 99% assessment likely was predicated), assumed no lights in trailing cars.  

Your definitive response to the change in assumptions is most helpful in my track planning.  I’ll follow the standard practice of making the AR segment longer than longest (lighted) passenger train. 

Bill D
N&W Steam Only


On Nov 6, 2021, at 9:08 PM, whmvd <vandoornw@...> wrote:


It matters very much. Fatally, for too long trains. Nobody would feed the interior lights off just one axle, and as soon as you have more than one the die is cast.

Wouter

On Sat, 6 Nov 2021, 19:17 D B, <1932mgj2@...> wrote:
Thanks John. 
I do understand and agree with your explanation.  Sounds like that is the basis for Wouter’s "99% of the time" assessment. 
Query, in your view (and for purposes of Wouter’s 99% assessment), does it matter whether the cars (passenger) are lit?
Bill D
N&W Steam Only





D B
 

Blair,
Thanks for the cautionary warning about future train length.  The passenger train is already 7+ feet long (maybe too long for my layout!).  It certainly won’t get any longer, not the least because the N&W passenger cars from the steam era are nearly impossible to locate (and I’m no longer looking)!
Bill D
N&W Steam Only


On Nov 7, 2021, at 7:55 AM, Blair <smithbr@...> wrote:



Bill

Sounds like you've discounted this option.  Keep it in mind, though, as should your desired train length increase, you'll otherwise run afoul of the AR length again.

Blair

On 2021-11-06 7:55, Blair wrote:

Well, if it's one train, perhaps consider plastic wheel sets on the last two or three cars, if you have problems? Just a thought.

On 2021-11-05 23:31, D B wrote:
Wouter, 
Thanks for the authoritative answers.  The minimum length issue is really critical to the design and operation of my layout.  My minimum length concern arose when I realized the N&W passenger train, pulled by a J, that I had painstakingly assembled and planned to be a signature hallmark of the layout was longer than one of my two AR segments. That appeared to require a fundamental reworking of my track plan.   However, the redesign would have imposed significant limitations on operations.  I believe I’ll accept the <1% risk in order to improve operational flexibility (including the realistic opportunity to run two trains simultaneously).
Your advice is greatly appreciated. 
Bill D
N&W Steam Only


On Nov 5, 2021, at 5:11 PM, whmvd <vandoornw@...> wrote:


Bill,

I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?

In practice, you will probably get away with longer trains with just metal wheels not connected electrically to other axles at least 99% of the time. In the remaining <1%, there may be a short reported - or not if you're lucky. If not, you won't even notice anything amiss at all. But it's still not a good idea. If you add in the system that some people use to stagger the gap between left and right rail (which I am 100% sure is pointless, but does no harm normally) then the 99% will drop significantly, in line with the length of the staggered bit.

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

That is certainly safe. Even one loco OF a powered consist is plenty. Shorter will work, but there is no set shortest distance. Stick to the length of your shortest loco and you'll be good (although if you push a train instead of pull things need to be looked into more carefully).

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

Q1 is about how one autoreverser works, whereas Q2 is about preventing two AR sections  from in-fighting. It's like asking for the difference between inflation and the exchange ratio between dollar and euro. They are both about money, but there is no other relation.

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

That is correct. It's all about not crossing both gaps simultaneously.

Wouter

 

Thanks in advance.  

Bill D
N&W Steam Only


D B
 

Wouter,

Thanks for this morning’s confirmation.  I’m pretty confident I’ve got this AR thing worked out — at least the basic principles.  Of course, the devil is always in the details in implementation — like the lighted vs. unlighted cars, or plastic (ugh) vs. metal wheels.  

 I had also posted (below) my assumptions related to operational limitations imposed by the presence of a turn out within the AR.  That limitation was to “avoid having a train cross the ‘AR gap’ at the turnout while another train is crossing the AR gap at one or the other of the two ‘ends’ of the AR segment.”  

May I assume from your silence that you also agree with that precaution?  

Thanks for your cogent advice and guidance.  No need to post a track plan. 

Bill D
N&W Steam Only


On Nov 7, 2021, at 12:15 AM, D B via groups.io <1932mgj2@...> wrote:

Given this limitation, my lengthened AR segment will now include a turn out.  I assume that, properly insulated, the only operational limitation the presence of the turn out presents is to avoid having a train cross the “AR gap” at the turnout while another train is crossing the AR gap at one or the other of the two “ends” of the AR segment.  
Bill D
N&W Steam Only


On Nov 6, 2021, at 9:08 PM, whmvd <vandoornw@...> wrote:


It matters very much. Fatally, for too long trains. Nobody would feed the interior lights off just one axle, and as soon as you have more than one the die is cast.

Wouter

On Sat, 6 Nov 2021, 19:17 D B, <1932mgj2@...> wrote:
Thanks John. 
I do understand and agree with your explanation.  Sounds like that is the basis for Wouter’s "99% of the time" assessment. 
Query, in your view (and for purposes of Wouter’s 99% assessment), does it matter whether the cars (passenger) are lit?
Bill D
N&W Steam Only





 

How about a variation on this theme of "back-to-back" ARs: I am planning a yard at the end of two legs of a Wye. It is a small yard and should only have one operator at a time (the Yard Master). So the problem of two locomotives crossing to into/out of the yard simultaneously has an extremely low probability. However, within this yard is a turntable that needs an AR. That creates an AR adjacent to an AR. I'm using PSX-ARs so the turntable can be the "Slave."
Does anyone see a problem with this setup?
Thank you,
Michael Boyle
Puget Sound, Washington


jfm2830
 

The problem with lighted cars (and locomotives) is the duration of the short between the 2 sections (the reversing section and either the section you are leaving or entering).  With just metal wheels the duration is very short, just the time the wheel bridges the gap, and the chance that both gaps are shorted simultaneously is very low.  But with lighted cars or locos, the front and rear trucks are connected so the short duration is the time while lead truck is one section and the rear truck is in the other section, is much longer. So the probability of having the gaps on both the entrance and exit of the section shorted simultaneously is much, much longer and the chance of a problem becomes almost a certainty.
I have been working on a museum layout converting it to DCC and I've seen this happen.  One of guys running a long passenger train tried to run thru the reversing section and ended up crashing the whole layout as the reversers couldn't handle it and the command station started shutting down and then restart, and then shutdown and restart, etc. until we turned everything off and cleared the train.
Good Luck, John Moonan


Scott H. Haycock
 



On 11/07/2021 11:57 AM Michael Boyle <boyle10017@...> wrote:


 ''That creates an AR adjacent to an AR.''

I think that if you look at this as an AR within an AR. the answer will be more apparent.

Scott Haycock