So if ABS was used on the

So if ABS was used on the mainline, it would continue through the yard?

That would seem somewhat restrictive to yard operations, especially a relatively small yard like St Johnsbury. I will have to give that some thought.

Thanks,

Chris

The problem is back and forth movement

The basic problem being solved with yard limits is back and forth movement.

Ordinarily, a train is expected to proceed in one direction from its origin to its destination. Backing up is forbidden without special permission, since it introduces all kinds of hazards to other trains.

Yard limits mostly means trains can move both directions without special permission, and any train entering yard limits needs to proceed at restricted speed, watching for other trains moving in any direction.

Also yard limit movements are often governed by a yardmaster.

On my prototype Siskiyou Line, the yard limits were signalled (permissive), and the signals simply added extra supplemental information to the trains operating within the yard limits as to the possible presence of another train.

Ok, that makes sense

I will set up to signal as per a normal siding.. but then be governed per yard limit rules.

This has come to mind since I have been doing a lot of study of signals for one reason or another over the last month and there were a few wrinkles (like this one) I could not find reference on. Wish I had bid just a little higher on the John Armstrong Signal book!

Thanks

Chris

Sorry guys, this is where my

Sorry guys, this is where my lack of railroad acronyms comes in, could someone tell me what ABS or where I can find referance to it, thanks

Absolute Block Signaling/Absolute Permissive Block Signaling

Absolute Block Signaling.. and the variant Absolute Permissive Block Signaling (APB).

This website  discusses signalling in general:

http://www.lundsten.dk/us_signaling/index.html

This section applies specifically to APB:

http://www.lundsten.dk/us_signaling/abs_apb/index.html

Thinking about it, permissive signals probably won't be a big issue for me. I wont have distances between sidings long enough to justify more then one block on my small layout, so I probably will have true ABS. Permissive just means that some red signals mean "stop and proceed slowly" rather then "stop and wait for green". Permissive signals are just an enhancement to the ABS system.

I think in stuff I read about real railroads, ABS is used often to describe areas that were actually permissive.

HTH,

Chris

Brilliant Chris, many thanks

Brilliant Chris, many thanks

Thanks Jerome. Your point is

Thanks Jerome. Your point is well taken. The signal system serves only one purpose in this. I think that the phrase "protected by APB signals" conveys that well!

My layout is going to be a relatively short run. I don't want to spend more time writing warrants then actually moving on the layout. I will dabble in DTC and TWC and see which feels better.

Chris

Absolute Block Signaling..

Actually, ABS stands for Automatic Block Signalling. ABS signals are Not absolute signals.

Absolute means Red = Stop. For most ABS signals Red = Stop & Proceed (at restricted speed). Under some rules, if there is a plate with an "R" on the signal mast, the indication is further modified to just a restricting (Proceed at Restricted speed).

Absolute-Permissive Signalling, while a variant of block signalling, really behaves quite differently than a simple ABS system. A regular ABS system just indicates block occupancy. APB actually provides full protection against opposing trains between siding switches. (When a train leaves a siding, the APB system detects which direction it's headed in, and throws every opposing signal up to the next siding to red.  ABS has no such capability to detect direction of movement and cannot protect opposing train movements, only following movements. CTC, Track Warrants or OCS must control the movement of trains in opposite directions.)

Thsnks!

Thanks for the clarification!

Most of the stuff I have read was about APB and discussed ABS as an aside. Thinking about it, the opposing train limitation is something of an advantage to me.. it allows me to put in an interesting signal system while still requiring some operational thought to get trains across the subdivision..

Chris

ABS and APB etc.

ChrisNH:

Well, that makes a certain amount of sense. If what you're reading was describing APB, you almost can't help but also mention ABS as an aside, since APB is conceptually a derivation and enhancement of ABS, which is the simpler system. ABS only tells whether the blocks ahead are clear or not, so it's perfect for model rr implementation. (in certain cases, like at siding switches, the signal indication will also depend on the position of the switch.)

ABS signals can be used as part of CTC (intermediate signals between interlockings or control points) or own their own in conjunction with either train orders, Track Warrants or OCS. They don't authorize movement, they just protect the rear of the train from following movements. In completely dark territory, more direct protection is needed. In TT&TO, the dispatcher can issue "wait at..." time orders to keep it behind another, and there are detailed rules on flagging protection if a train is forced to stop somewhere. In modern days, an OCS clearance (or track warrant) can direct the train to "protect against" the preceding train, requiring both trains to work out their own protection over the radio.

Yard Limit Authority

The advantage of Yard Limits is that no Authority is required to use the Main Track.  In areas where there is a lot of industry switching, this allows a Road Switcher to enter and leave the main track without bothering the dispatcher for orders or track warrants.  Yard Limits also eliminate the need for Rule 99 flag protection.

The problem is that Yard Limits require operation at Restricted Speed which delays through traffic.

The solution is to install ABS (AUTOMATIC Block Signals) which allow through trains and local traffic to operate through Yard Limits on Signal Indication at Track Speed.

Note that CTC or any system using Absolute Signals requires Authority from Signal Indication or Verbal Authority from the Dispatcher or Control Operator.  Red Automatic Signals can be passed at restricted speed after stopping.  ABSOLUTE signals convey Authority.  AUTOMATIC signals do not.

To enter the main track in ABS territory, you throw the switch and wait five minutes in case another train has already gone past a signal.  This assures that the block is protected.  Again, Authority to enter the main track comes from a time table, train order, track warrant, or yard limits.

yard limits

ABS (which will include APB since there is no difference in authority) can extend through yard limits. What yard limits do is allow trains and engines to occupy the main track clearing 1st class trains and not protecting against others ( if you are in an era that has 1st class trains). If a train or engine can't clear the time of a first class train they have to protect against it. The first class train may operate at track speed and all other movements are at something like restricted speed. What ABS does for you is many rule books provide that in yard limits if the main track can be.seen to be clear and switches lined, trains and engines can proceed at track speed. Rule books permit a block signal displaying a signal better than approach as evidence the main is clear and that the switches are lined. The down side is that trains and engines entering the main track in ABS may be required to observe the waiting times.

Kinda sorta maybe

""The advantage of Yard Limits is that no Authority is required to use the Main Track. In areas where there is a lot of industry switching, this allows a Road Switcher to enter and leave the main track without bothering the dispatcher for orders or track warrants. Yard Limits also eliminate the need for Rule 99 flag protection."

Not quite, if you are in an era with first class trains, and the "traditional" definition of yard limits, if you can't clear the times of the first class train then you still have to provide flag protection in yard limits.

"The problem is that Yard Limits require operation at Restricted Speed which delays through traffic."

Unless its a first class train with the traditional definition or there is a block signal system and the rules permit operating a a speed better than restricted if the signals display an indication better than approach.

" The solution is to install ABS (AUTOMATIC Block Signals) which allow through trains and local traffic to operate through Yard Limits on Signal Indication at Track Speed."

Provided they have an indication better than approach.

"Note that CTC or any system using Absolute Signals requires Authority from Signal Indication or Verbal Authority from the Dispatcher or Control Operator. Red Automatic Signals can be passed at restricted speed after stopping. ABSOLUTE signals convey Authority. AUTOMATIC signals do not."

It requires a proceed indication or verbal authority and CTC to be in effect.  There is no difference in the rules between a stop indication in CTC and a stop indication in ABS.  They are both stop signals.  There is no mention of an "absolute" signal.  The only place "absolute" comes into play is that if a signal mast diplays a sign with an "A" on it, it means the most restrictive signal it displays is stop (as opposed to stop and proceed). The difference is how trains proceed from a stop indication.  The process to pass a stop indication is different in CTC vs. ABS, the signals are not.  Name Stop, aspect: Stop,  indication: Stop.

The signals that can be passed after stopping or passed at restricted speed are intermediate signals (not automatic) that display stop and proceed or restricting indications (or grade in some areas).  If you look in a rule book they will almost never refer to an "absolute stop" signal and they don't refer to "automatic" signals.

"To enter the main track in ABS territory, you throw the switch and wait five minutes in case another train has already gone past a signal. This assures that the block is protected. Again, Authority to enter the main track comes from a time table, train order, track warrant, or yard limits."

I would agree with all of the above, with one little caveat.  In rule 251, current of traffic territory (which was an extremely common system on double track) the signal system was ABS  (not CTC) and after a train was cleared, a proceed signal in ABS was authority to occupy the main track (no train orders required).

CTC stop vs. ABS stop and proceed

Dave 1905 wrote:

" There is no difference in the rules between a stop indication in CTC and a stop indication in ABS.  They are both stop signals.  There is no mention of an "absolute" signal.  The only place "absolute" comes into play is that if a signal mast displays a sign with an "A" on it, it means the most restrictive signal it displays is stop (as opposed to stop and proceed). The difference is how trains proceed from a stop indication.  The process to pass a stop indication is different in CTC vs. ABS, the signals are not.  Name Stop, aspect: Stop,  indication: Stop."

​Our BNSF and UP signals do have Absolute signals that have no number plate or the "A" plate and display a stop indication (BNSF Rule 9.1.15, UP Rule 9.2.15).  Automatic signals, including CTC intermediate signals, have a number plate and display a "stop and proceed" (BNSF Rule 9.1.14).  UP has recently renamed "stop and proceed" to "restricted proceed" (Rule 9.2.14).  Reference current UP and BNSF System Special Instructions (SSI).

The important thing about an Absolute Stop is that it requires Authority from a Dispatcher or Control Operator to pass.  CTC signal authority replaces Time Table authority.  These are present day definitions.  If the rules were different in Time Table & Train Order (TT&TO) days, reference should be made to appropriate documents.

Things change.

"Absolute" Stop

This is where people get confused in the rules when you add stuff that isn't there.

UP rule 9.2.15 is named "Stop" and it's indication is "Stop before passing any part of train or engine passes the signal."

Old UP rule 9.2.14 was named "Stop and Proceed" and it's indication is "Stop before  any part of the train passes the signal then proceed at restricted speed to next signal."

There is no mention of "absolute" or "automatic" in either of those rules.  There is also no differenciation between ABS and CTC signals.  The same rules and indications apply to both systems.  One also has to be careful about the era.  As mentioned above, if you go back 5 years or so on the UP, "restricted" was named "stop and proceed".  If you go back a couple decades, a stop signal in ABS required a train to contact the dispatcher and get permission to pass it.  For example the UP 1972 Rules, the first paragraph of rule 509 in the Automatic Block Signal System rules reads:

"509. When a train or engine is stopped by an automatic block signal indicating Stop, and such indication does not change promptly to a more favorable indication, a member of the crew must immediately communicate with the train dispatcher and be governed by his instructions."

While the first sentence of the CTC rules regarding movement from a stop signal read:

"269.  When a train or engine is stopped by a Stop signal, and no conflicting movement is evident, a member of the crew must immediately communicate with the control operator and be governed by his instructions."

Note the similarities.  The big difference is in what happens if communication cannot be established with the dispatcher or control operator.  In ABS, if the train has authority beyond the stop signal, the train can pull past the signal, wait 5 minutes, then proceed at restricted speed.  In CTC the train may not pass the stop signal.

In either case the signal indication was the same, stop, the difference wasn't in the signal, it was in the rules that govern movement past those signals.  If I saw a picture of a stop signal, I could not, just form the picture of the signal itself, tell you whether it was in CTC or ABS.

Era & railroad

Era and railroad often are critical in railroad rules discussions.  There are certain broad concepts that cut across eras and roads, but when discussing specifics, era and road can be critical.

For example, the discussion on stop and proceed signals.  Just in the last 30 years there have been at least 4 different variations on the UP (and predecessor lines).  

Originally a stop and proceed signal meant stop, then proceed at restricted speed to the next signal.

At some point it was changed to stop, then proceed at restricted speed to the next signal and pass any subsequent stop and proceed signals at restricted speed without stopping.

Then it was changed to not require a stop at all, just proceed at restricted speed to the next signal.

Finally the name was changed to restricted proceed, just proceed at restricted speed to the next signal.

Specifying an era and railroad or an edition of a rulebook really helps focus the discussion, since, as with the above example, two people could be arguing over whether a stop and proceed signal requires a train to stop and if nobody identifies the context, they both could be right.

Yard lead signal for main line entry.

50 years ago at Oakland, CA the SP had signal protection to allow or prevent anything coming off the yard lead, at the A/D tracks, onto the main line. John

yard lead signal

If its truly ABS (not CTC or an interlocking or have a special instruction) then a stop signal into yard limits wouldn't keep a train from entering the main. That's the whole point of yard limits, to let trains onto the main.  You have to figure that the train will get a stop signal 100% of the time.  In ABS the switches are in hand throw operation.  Main track switches must be lined for main track movement when not in use.  So pretty much every train pulling up to the main track switch will get a stop signal because every train pulling up to the switch from the yard will find it lined against the train.  IN ABS the dispatcher can't line switches or signals.  In yard limits trains an engines can occupy the main track without getting authority from the dispatcher.

The SP might have had a signal but it wasn't an ABS signal, it was probably a manually controlled signal which makes it a de facto interlocking or CTC operation.  The SP had a lot of one off stuff in their rules.  If you read Josserand's "Rights of Trains" there are several discussions of how the SP differs in several areas.