What is a 'Dark' area?

[dibber25]

I'm interested in finding out more about what a Canadian friend calls 'dark areas' - as in train control/signalling. I guess this is an area without track circuits - in other words it is 'dark' on the CTC control panel and all movements are governed by train orders and radio despatching? Am I right? Where can I find out more? How widespread are they and are there many which are used by passenger trains?

CHRIS LEIGH

[Kenton]

http://en.wikipedia.org/wiki/Glossary_of_North_American_railway_terms under D

[CraigZ]

Yes, 'dark' territory has no signals and movements are governed by train orders, given nowadays over radio. On Norfolk Southern they are called 'track warrants'.

 

By FRA rules the maximum speed in dark territory is 49 mph if the track condition permits...so not terribly conducive to passenger train operation. Having said that, the Piedmont and the Carolinian ran about 110 miles in dark territory from Selma, NC to Greensboro NC (save for a 7 mile stretch in Raleigh/Cary) until just a few years ago.

[signalmaintainer]

Yes, 'dark' territory has no signals and movements are governed by train orders, given nowadays over radio. On Norfolk Southern they are called 'track warrants'.

 

Don't mean to be pedantic, Craig, but dark-signal territory can have signals, for instance in areas where there are slide fences. An example is BNSF's Gateway Sub. It's dark territory and TWC between Keddie, Calft., and Klamath Falls, Ore. Wayside signals alert crews when the slide fences are down.

 

Dark-signalled territory can also have track circuits; an example is again part of the signal-control circuit in slide-fence areas. Typically it's a low frequency (under 1000 Hz) signal with an 8-bit data block sent via a transmitter (an oscillator) through the rails to a receiver. The receiver's output drives a relay. If the transmitter goes down, e.i., the slide fence breaks which interrupts the energy to the transmitter, it stops sending out information. When the receiver no longer gets the expected information, it removes energy to the relay and a signal aspect indicating the slide fence is down is displayed.

 

The best description of dark territory is that it's those areas not equipped with Automatic Block Signaling/APB or CTC.

[dave1905]

People get dark territory confused all the time. One has to separate the signal system from the authority system.

 

Dark territory is territory with no block signal system in effect.

 

Manual Block territory has a manual block system in effect (somewhat similar to British "singla boxes").

 

Automatic block signal territory has a block signal system in effect.

 

Then there are the authority systems.

 

Timetable and train order grants authority based on a timetable schedule or train order.

 

Track warrant grants authority based on track warrants (there are a variety of variations know by other names).

 

Direct Traffic control grants authority based on blocks.

 

Current of traffic grants authority on signal indication in the current of traffic.

 

Centralized traffic control grants authority based on signal indication at controlled signals (there are a variety of variations known by other names).

 

Interlocking grant authority based on signal indication.

 

A critical part of studying "dark territory" is establishing an era and control method because in the mid 1980's the authority systems changed radically and the rules and concepts before the change in many cases are not anything like the rules afterwards.

[CraigZ]

Don't mean to be pedantic, Craig, but dark-signal territory can have signals, for instance in areas where there are slide fences. An example is BNSF's Gateway Sub. It's dark territory and TWC between Keddie, Calft., and Klamath Falls, Ore. Wayside signals alert crews when the slide fences are down.

 

Dark-signalled territory can also have track circuits; an example is again part of the signal-control circuit in slide-fence areas. Typically it's a low frequency (under 1000 Hz) signal with an 8-bit data block sent via a transmitter (an oscillator) through the rails to a receiver. The receiver's output drives a relay. If the transmitter goes down, e.i., the slide fence breaks which interrupts the energy to the transmitter, it stops sending out information. When the receiver no longer gets the expected information, it removes energy to the relay and a signal aspect indicating the slide fence is down is displayed.

 

The best description of dark territory is that it's those areas not equipped with Automatic Block Signaling/APB or CTC.

 

I'm in eastern North Carolina about 400 feet above sea level - what's a rock slide?

 

:)

[dave1905]

As far as how widespread it is, for example on the UP about 1/3 the railroad is CTC, 1/3 ABS (block signals but authority is granted with track warrants) and 1/3 "dark" no block signals (authority is yard limits, TWC, etc.)

 

 

[dave1905]

If you are looking at the modern era, train orders are not used, the two most common methods are direct traffic control (DTC) and track warrant control (TWC). Dirrent railroads or rule books have "branded" the two types of operation but there are a lot of common elelments between them.

 

The basic difference between the two types, DTC vs. TWC, is the how the limits of the authority are doled out. In DTC the railroad is permanently broken into fixed "blocks" that are marked with signs. Each block is named. Authority is issued by listing the blocks a train can occupy. In non-block signal teritory on one train can be in any one block without joint authority. The way I describ it to modelers is it operates like old school, conventional DC block toggle operation. You assign the main in descrete blocks and only one track can operate in that block at a time.

 

On the other hand in TWC and its breathern, authority is granted between two identifiable points. They can be mileposts, stations, switches, yard limits, etc. The limits can be as long or as short as necessary. the limits are noted on a fill in the blanks form. In non-block signal territory only one train can occupy the limits without joint authority. It operates a lot like DCC on a "mother may I" type layout operation where the dispatcher verbally instructs trains where to go.

 

Obviously these descriptions are greatly simplified, but they are the major differences.

 

If you are looking at train orders, that is whole nuther bag of worms and has completely different concept on how authority is managed.

[signalmaintainer]

I'm in eastern North Carolina about 400 feet above sea level - what's a rock slide?

 

:)

 

A rock slides a distance inversely proportional to its size, which is directly proportional to the magnitude of pain in your foot after you kick said rock.

[lonesome_whistle]

 

If you are looking at train orders, that is whole nuther bag of worms and has completely different concept on how authority is managed.

 

It's a bit of an alien concept for those of us brought up on British signalling systems too. If anyone is interested in finding out more about train orders, I would recommend 'Rights of Trains' by Peter Josserand. Be warned its 450-odd pages will provide several month's of bedtime reading if digested properly!

[Gerald Henriksen]

The Canadian Transportation Safety Board report into the derailment/crash of a VIA train in 1999 in dark territory appears to provide the info you are interested in:

 

http://www.tsb.gc.ca...07/r99h0007.asp

 

It describes what dark territory is, the Canadian rules that govern it, as well as having a listing (as of 2001) of the dark territory used by VIA trains and the speed limits (up to 95 mph in some cases).

[dave1905]

It tells some general information about dark territory, but really very little about how it is operated. You couldn't use that report to determine how to operate a model railroad.

[Oldddudders]

I'm quite glad that "those who know" are demonstrating just how complex US signalling systems can be, because, as suggested above, we who have some knowledge of UK systems find it all a bit of a mystery. Model Railroader, and Andy S in particular through his "Operators" column, has done its best to peel the onion skins a bit, but I'm still lost in the fog. It is not helped by the unrealistic frequency of traffic on most model railways, which in the real US would justify installation of CTC, but in model-form TT and Train-Orders seem to be much more fun - and more in keeping with a transition-era theme.

[signalmaintainer]

I'm quite glad that "those who know" are demonstrating just how complex US signalling systems can be, because, as suggested above, we who have some knowledge of UK systems find it all a bit of a mystery. Model Railroader, and Andy S in particular through his "Operators" column, has done its best to peel the onion skins a bit, but I'm still lost in the fog. It is not helped by the unrealistic frequency of traffic on most model railways, which in the real US would justify installation of CTC, but in model-form TT and Train-Orders seem to be much more fun - and more in keeping with a transition-era theme.

 

I've had the privilege of operating some very fine layouts here in the U.S. which use timetable/trainorders for operation. The lack of signals, apart from train order signals at depots or automatic interlockings (first-come, first-served), makes them seem a tad spartan, though. And there are times when the era in which the layout is based justifies the use of Automatic Block Signaling, but the owner has not installed it yet, creating an anachronism for the pedant.

 

I've been of the mind that were I to go back to U.S. outline with some kind of main line, I'd opt for an operating scheme based on train orders/track warrants with Automatic Block Signaling -- or even Absolute-Permissive Block, a more complex version of ABS. One gets the best of both worlds this way -- a dispatcher to give authorities to trains to move from Point A to Point B, and signaling to protect those movements and govern speeds, with train crews looking at the signals and their authorities.

 

An example of the above would be the SP&S in the late 1960s or BN in the 1970s/1980s on what is today BNSF's Fallbridge Subdivision. Or the Milwaukee Road over the Cascade Mountains in 1960s-1970s. Each had ABS with train orders/track warrants.

[Adrian Wintle]

As an example, when I was riding on the GO Barrie line a few years ago, the line was dark from a point just outside the city (Snider North) to Barrie. At the time there were four northbound trains in the afternoon (no southbound traffic - single line with no passing loops). The first train would be authorized to enter the area as part of its initial paperwork. When they reached Aurora (about half way to Barrie and about 1/3 of the way through the dark area), they would radio back to the following train, allowing it to enter the dark area. Likewise, the second train would radio back to the third, etc. I don't know for sure, but I presume there was a second clearance point somewhere north of where I got off the train in Newmarket. I tended to sit at the front of the cab car, so I got to hear all this and I got to chat with the crews.

 

Adrian

[dave1905]

Since this thread is about "dark territory" (NO signals) and the accident report was about a Canadian accident in "dark territory" how does this ilustrate how complex ***US*** signalling systems are?

 

First off y'all enter the conversation assuming that US signalling systems are complex, therefore you make them complex. The UK systems are just as baffling to somebody from the US as the US systems are to somebody from the UK. UK signals can't be too easy, you have an entire section of this forum dedicated to helping people figure out where to place them and most threads give 3 or 4 options on how to arrange them.

 

7 signals will cover 90-95% of the signalling situations in the western half of the US:

Stop

Stop and Proceed/Restricting

Approach

Diverging approach

Advance approach

Clear

Diverging Clear

 

[dullsteamer]

Dave, I think it's not so much that UK modellers find the actual signalling complex, rather that they lack understanding of the underlying rules and procedures that govern their operation. I run trains for a living here in Australia, and even I sometimes have to think twice about how things are done on US railroads - and we've adopted a lot of your procedures and terminology over the last 20 years.

[The Stationmaster]

Part of the problem in understanding some overseas signalling systems, and vice versa, is the need to discriminate between route signalling and speed signalling. If you at least appreciate that such a difference exists you stand a better chance of understanding what the aspects mean. So research always pays dividends - I would have been mighty puzzled by signal aspects in the Sydney (NSW) 'inner' area if I hadn't read up the basis of it before I saw it - but I had and it made perfect sense when I actually saw it in operation. Same for the USA - start from the fact that it's speed signalling and it begins to make sense.

[dullsteamer]

Interesting that you should make this observation, Mike. I've just returned from a holiday in Melbourne, where amongst other things I spent a day "playing trains" with a mate of mine who is a driver trainer there. It took me a while to get my head around their signals, which are speed signals.

 

But now you've got me wondering - what signal aspects of ours in Sydney would you have been puzzled by?

[dave1905]

 

I've been of the mind that were I to go back to U.S. outline with some kind of main line, I'd opt for an operating scheme based on train orders/track warrants with Automatic Block Signaling -- or even Absolute-Permissive Block, a more complex version of ABS. One gets the best of both worlds this way -- a dispatcher to give authorities to trains to move from Point A to Point B, and signaling to protect those movements and govern speeds, with train crews looking at the signals and their authorities.

 

 

I would take a different tack on the ABS signals.

 

First there has to be made a distinction between prototype and model operation. The critical things that ABS does for a prototype railroad are not as critical in a model setting. Models don't have to worry about broken rails, open switches, or running into the train ahead as much as the prototype. Since the model systems have much better stopping power and the person operating the train has tremendously better range of vision than the prototype, all the things an ABS system does for the prototype are pretty much moot on the model.

 

From the standpoint of how trains operate, a timetable and train order layout with ABS will operate exactly the same as a timetable and train order layout without ABS. The trains will get the same orders, the trains will move in the same way, the meets and passes will be the same. About the only difference is with ABS, if somebody leaves a main track switch open the next train will get a warning.

 

On the other hand if you are operating with DTC or track warrants (the OCS mentioned in the Canadian accident report is a variation of track warrants) the ABS gives you a significant advantage if you are operating without cabooses. The advantage is that since the signaling system provide the equivalent of flag protect against a following train, an ABS system allows multiple warrants to be issued for the same limits for trains in the same direction. Without ABS, only one train can be in the limits at a time (unless the limits are joint). I often advise people to use track warrants and pretend they have an ABS system. That gains them the utility of allowing multiple following moves (bunching is a good thing on a model railroad). Other than that, for a model railroad, the ABS system doesn't really add any practical advantage over a dark railroad.

 

Once again, ABS on a prototype railroad provides a large step in safety. It could have prevented, or at worst reduced the severity, of the Canadian accident example. My comments on it not being useful are directed at a model railroad applications, NOT the prototype.

 

By the way, virtually all the US signal systems are actually APB and in most cases when rules talk about ABS, they mean APB. For my purposes I consider them interchangeable, when I say ABS, I mean APB.

[dave1905]

When they reached Aurora (about half way to Barrie and about 1/3 of the way through the dark area), they would radio back to the following train, allowing it to enter the dark area. Likewise, the second train would radio back to the third, etc.

 

In the US that is called "Radio Blocking" (General Code of Operating Rules 14.4.1). It is not universally used on US railroads. For example it is rare (if used at all) on the UP.

[The Stationmaster]

Interesting that you should make this observation, Mike. I've just returned from a holiday in Melbourne, where amongst other things I spent a day "playing trains" with a mate of mine who is a driver trainer there. It took me a while to get my head around their signals, which are speed signals.

 

But now you've got me wondering - what signal aspects of ours in Sydney would you have been puzzled by?

Sorry to go OT - the first puzzle would have been the meaning of the lower red, until you realise that when colour lights came along in NSW distant signals still showed a red light at caution so in fact the lower red is a distant signal at caution and not a stop signal at danger. The sort of equivalent of a warning signal in British practice - the miniature green when the main heads are showing two reds also makes a lot more sense when you know how it works and relate it to timetable frequencies on the City loop (and was duly I photographed when I took pics through a full aspect sequence at Circular Quay one Saturday afternoon - how else would I spend my day off ).

[dibber25]

Didn't mean to open a can of worms here, and there's certainly no need for a debate over whose system is most incomprehensible! Truth is, signalling in any country is a bit of a mystery to most people unless they actually take an interest in trying to understand it. I recall watching 'Brit' enthusiasts on a train in 2006 trying to figure out what the signal indications in Canada meant and applying a British - and entirely wrong - supposition. In fact, my interest in 'dark areas' is professional, with my non-modelling hat on, as I wanted to understand a bit more about Canadian railway operation. That TSB report is, in fact, extremely interesting in that it draws attention to a practice (local hand-operation of points, without any advance indication of how they are set) which is open to someone simply forgetting to reset them to the main line. There is thus a risk element which could be acceptable on a freight railway and where speeds are low but surely becomes unacceptable on a passenger line with 80mph speed limit.

But this is a modelling forum - sorry to divert from core principles.

CHRIS LEIGH

[signalmaintainer]

I would take a different tack on the ABS signals.

 

First there has to be made a distinction between prototype and model operation. The critical things that ABS does for a prototype railroad are not as critical in a model setting. Models don't have to worry about broken rails, open switches, or running into the train ahead as much as the prototype. Since the model systems have much better stopping power and the person operating the train has tremendously better range of vision than the prototype, all the things an ABS system does for the prototype are pretty much moot on the model.

 

From the standpoint of how trains operate, a timetable and train order layout with ABS will operate exactly the same as a timetable and train order layout without ABS. The trains will get the same orders, the trains will move in the same way, the meets and passes will be the same.

 

True, but that's really not the point, is it? If the prototype line being modeled had ABS, then fidelity to the operating mode in a model railroad would require ABS. A microprocessor could be added to randomly introduce signal indications for broken rails and broken slide fences, with crews required to operate accordingly. Open switches are just as easily modeled -- it's just a 1 or a 0 into the processor. For the crews it's more realism and hence all part of the fun.

 

From your standpoint, CTC signalling -- for that matter, any signalling -- would appear to be superfluous on a layout, because after all crews have a much better (and unprototypic) range of vision.

[signalmaintainer]

Didn't mean to open a can of worms here, and there's certainly no need for a debate over whose system is most incomprehensible! But this is a modelling forum - sorry to divert from core principles.

CHRIS LEIGH

But this is a prototype-related section on the forum for US/Canadian railroading topics. No diversion that I can discern!