U.S. signaling questions?

[signalmaintainer]

I've been the grateful beneficiary of many a member's help with understanding UK signalling, especially of the sadly disappearing manually operated semaphore and signal cabin era, which gave British railroading so much of its character.

 

So, in turn, please fire me a PM or post a question here if you have a question about U.S. signaling. I don't know everything, but I can get answers. The modern-era stuff is especially pretty easy, as it's what I do for a career with BNSF Railway in Seattle.

[trisonic]

Thanks, Paul. It's a kind offer. Is it possible to have a wee primer to get the ball rolling?

The concepts of Home and Distant the same as the UK, in the development of modern signalling, for example?

 

Best, Pete.

[signalmaintainer]

Over here, Pete, Distant signals are used only in approach to mainline signaled territory (Centralized Traffic Control or Automatic Block System) from non-signaled territory. Distants can never display a "Stop" indication and indicate what the signal in advance will be.

 

All signals controlling entrance into a block are considered Home signals. Signals displaying a number board (usually the milepost is part of the number) are considered Permissive -- trains must stop and then can proceed at restricted speed (20 mph or less) to the next block. All other Home signals not displaying a number board are Absolute signals -- trains must stop.

 

In CTC territory, trains can move on signal indication. In ABS territory, signals only provide block occupancy status and authority is granted via a track warrant from the dispatcher. In ABS, the DS cannot line routes nor call signals.

 

That's a really brief overview of modern US signaling.

 

 

[F-UnitMad]

Signalling is one of those complex subjects that is very often almost ignored altogether, especially as for most layouts it isn't really needed for operations, unlike on real railways, and I suppose many of us Brits especially have concentrated on the "One Engine Short Line" side of US Railroading which may possibly avoid the subject altogether (obviously there must be exceptions!!) too...!!

 

What would be very helpful would be some photos of typical US signals and an explanation of what they are/do, and where they would be placed. I'm thinking of things like those colour-light (sorry, color-light) "target" signals(?) where there's three in a vertical row, and they only seem to show red..?

As you can tell, I know zip about this subject....

[BR60103]

I have an old Canadian rule book and I posted the signalling pages somewhere (I thought they were here). I can repost if necessary.

In the Canadian system, the signals give speeds.

A single head can show Green, Flashing Yellow, Yellow, or Red. Clear, Advance Clear to Stop, Clear to Stop, Stop and Proceed at restricted speed. (2 variations if there's a sign on the post).

3 heads can give a lot more information, especially covering interlockings. Rule 413 is Red over Flashing Green over Green -- Limited to Medium --Proceed, limited speed passing signal and through turnouts, approaching next signal at medium speed. (Limited:<=45 mph, Medium <=30 mph.)

[signalmaintainer]

I have an old Canadian rule book and I posted the signalling pages somewhere (I thought they were here). I can repost if necessary.

In the Canadian system, the signals give speeds.

A single head can show Green, Flashing Yellow, Yellow, or Red. Clear, Advance Clear to Stop, Clear to Stop, Stop and Proceed at restricted speed. (2 variations if there's a sign on the post).

3 heads can give a lot more information, especially covering interlockings. Rule 413 is Red over Flashing Green over Green -- Limited to Medium --Proceed, limited speed passing signal and through turnouts, approaching next signal at medium speed. (Limited:<=45 mph, Medium <=30 mph.)

 

US signaling is primarily speed-signaling based as well. When an aspect for a diverging route is displayed, it's shown as a red over green, red over flashing yellow, red over yellow or red over flashing red.

[signalmaintainer]

Signalling is one of those complex subjects that is very often almost ignored altogether, especially as for most layouts it isn't really needed for operations, unlike on real railways, and I suppose many of us Brits especially have concentrated on the "One Engine Short Line" side of US Railroading which may possibly avoid the subject altogether (obviously there must be exceptions!!) too...!!

 

What would be very helpful would be some photos of typical US signals and an explanation of what they are/do, and where they would be placed. I'm thinking of things like those colour-light (sorry, color-light) "target" signals(?) where there's three in a vertical row, and they only seem to show red..?

As you can tell, I know zip about this subject....

 

I'll see what I can drum up. As for the color-light signals showing only red, most likely those are at a CTC control point. The dispatcher must request the signal and, based upon codes received from the signal in advance, the color-light can show a less-restrictive aspect.

 

So, while the dispatcher can request a signal or set a cleared signal to stop at a control point (with a resulting time penalty before they can clear another signal at that control point), they have no control over what aspect the signal displays (other than when a signal is set to "stop" it displays red). The aspects are dependent upon the "vital" signal logic, be it relay-based, microprocessor-based, or a combination.

 

Aspects for intermediate signals between control points in CTC territory and distant signals are dependent solely upon upon vital codes coming from the signal in advance. Dispatchers have no control over these signals and do not even see them on their screens.

[trisonic]

Paul, Are there any reference books on this subject in the 'States that are halfway accurate? Worth an addition to the well-thumbed part of our libraries? I must admit I find the target signals on our local NS and CSX mainline routes very confusing..........

 

Best, Pete.

[signalmaintainer]

Paul, Are there any reference books on this subject in the 'States that are halfway accurate? Worth an addition to the well-thumbed part of our libraries? I must admit I find the target signals on our local NS and CSX mainline routes very confusing..........

 

Best, Pete.

 

There is, Pete. Although written by a layman, "Railroad Signaling" is accurate and gives a good overview of US signaling practice: http://www.amazon.com/Railroad-Signaling-Brian-Solomon/dp/0760313601

 

My boss even has a copy in his office, just for light reading!

[PhilH]

Thanks for offering to do this. I'm interested in steam/steam-diesel transition era signalling and am confused by the whole thing! I don't quite get why some lines were signalled and some not. I think I understand about trains being run by despatchers, but what governed which system was used?

 

I think that semaphores would have been in use during the time I'm interested in, but am not sure what displayed aspects mean for these. Are you aware of any books which would explain the whole thing about old school signalling please?

[CraigZ]

Rulebook pages, these from the Seaboard Coast Line rulebook dated 1 Jan 1981....there is of course other rules that govern movement in non signalled territory.

 

 

 

 

 

 

 

 

[dave1905]

Thanks for offering to do this. I'm interested in steam/steam-diesel transition era signalling and am confused by the whole thing! I don't quite get why some lines were signalled and some not. I think I understand about trains being run by despatchers, but what governed which system was used?

 

I think that semaphores would have been in use during the time I'm interested in, but am not sure what displayed aspects mean for these. Are you aware of any books which would explain the whole thing about old school signalling please?

 

Buy a rule book for your era snd railroad of interest. That will give the signal rules and the arrangements of signals for that specific railroad.

[dave1905]

All signal systems started out as manual block. In the late 1800's the US and British systems diverged. The US went towards an automatic block signal system and the British stayed with the manual block signal system.

 

In the US there are two basic types of signalling systems; ABS - Automatic Block Signals and CTC-Centralized Traffic Control

 

(ABS on all but the very earliest lines is actually an "APB" system, more on that later).

 

ABS and CTC do different things and the signals are placed in different places along the right of way.

 

You also have to remember that the US railroads were (except for the years around WW1) private companies so they could develop their own rules within general Federal regulations.

[JWB]

In my own (flawed, layperson's) view, the sanest discussion of signaling is in Bruce Chubb's How to Operate Your Model Railroad (Kalmbach), long out of print but available pretty cheaply used from Amazon (see http://www.amazon.co...06592681&sr=8-2 )

 

I've found that modelers tend to need to see the forest, while professional railroaders are necessarily focused on the trees. I've been interested in European/UK railroads as well as US railroads, including signals, and actually I don't think there's that much difference.

 

The traditional European and UK view is that every station is a "yard" in the sense of a "Bahnhof". Interlocking signals let trains in and out of the "Bahnhof" or station. Stations in the US are mostly much less formal affairs, so you don't have a signal box at both ends and a bunch of interlocking signals at each end -- and there have been some bad accidents here as a result, but that's something else. On the other hand, in the US, you do have interlockings, which work pretty much the same way. Interlockings occur at junctions, crossings, and other fancy trackwork. Before maybe 1960, each interlocking had a tower that worked like a signal box in the UK and governed signals that let trains in and out of the interlocking territory.

 

Interlocking signals are absolute: red means stop. Period. In a simple case where one line crosses another, the operator is allowed to set a route for one track in one direction, which can get a green or proceed signal. All other signals are red, and all other trains approaching the reds must stop. CTC signals are basically just a special case of interlockings, with the tower operator replaced by a guy a thousand miles away at a computer. It's worth pointing out that interlockings with signals can occur on a line that otherwise has no block signals (or in the past, no CTC signals). I think it's easiest to see the interlocking as the most basic unit of US SIGNALS (not operation, since you can operate without signals).

 

Semaphore vs light signals are just special cases. Semaphores with square ends are typically interlocking signals. Light signals with two or three vertical heads are also typically interlocking signals. They work the same way, you MUST stop at a red.

 

Non-interlocking signals are basically "permissive", which means that, depending on the particular rules, you must typically stop at a red but then proceed at restricted speed. Block signals are typically permissive, and they sort of correspond to distant signals between stations in the UK and Europe.

 

Whether a line has signals or not, and whether the signals are CTC, ABS, manual block, or other, depends partly on traffic and partly on other circumstances. A major wreck, for instance, could prompt the ICC to order CTC signals to be installed on a certain territory for political reasons even if the traffic didn't justify it. And ordinary prudence often required railroads to have towers and corresponding signals at interlockings for crossings of lines that weren't otherwise signaled.

 

The former Southern Pacific Coast Route was a fascinating patchwork of different signal and operating schemes. It was mostly train order and timetable operation with a block signal system overlaid, but there were "islands" of CTC. There's no single answer to anything with signals, but on the other hand, prototypes give a great deal of flexibility, depending on the railroad, the situation, and the era.

[PhilH]

Thanks for replies to my query - have ordered the Kalmbach book.

[signalmaintainer]

You also have to remember that the US railroads were (except for the years around WW1) private companies so they could develop their own rules within general Federal regulations.

 

That's a really important point for you guys modeling or interested in a specific US or Canadian prototype. A signal aspect might be identical on, say, the BNSF and UP, but the name and indication (the information the aspect conveys) can be different.

 

So, while the FRA has involved itself in almost every aspect of US railroading, it has not yet seen fit to mandate a national standard aspect-and-indication chart. In my opinion, it should, but that's a different topic.

 

When Dave dives into explaining APB (Absolute-Permissive Block) signaling, you'll find it's really the most complicated system of all. He committed to it so I'll defer to him!

[dave1905]

I've found that modelers tend to need to see the forest,

 

But in my experience they get really lost in the trees. 8-)

 

I've been interested in European/UK railroads as well as US railroads, including signals, and actually I don't think there's that much difference.

 

There are significant differences, especially with ABS, but there are more similarities than many people in the EU or UK often want to admit.

 

Interlocking signals are absolute: red means stop. Period.

 

STOP signals at interlockings are absolute. A STOP signal means stop. Interlockings can give permissive signals if conditions warrant.

 

CTC signals are basically just a special case of interlockings, with the tower operator replaced by a guy a thousand miles away at a computer.

 

Its a little more than that. An interlocking is a "point solution" while CTC used to authorize trains over long distances. An interlocking is a hundred feet to a couple miles long, while CTC can literally cover a thousand miles. Portions of CTC are like interlockings (the "control points", CP's) but the track between the CP's is ABS. CTC can also be controlled by "control operators" (the term used in rule books) who can be located along the CTC area.

 

It's worth pointing out that interlockings with signals can occur on a line that otherwise has no block signals (or in the past, no CTC signals). I think it's easiest to see the interlocking as the most basic unit of US SIGNALS (not operation, since you can operate without signals).

 

Normally the progression is dark, ABS, CTC. Whether it is the most basic or not could be debated, ABS doesn't require any "operator", being automatic, so could be considered the most basic from one standpoint.

 

Semaphore vs light signals are just special cases.

 

Semphores versus lights are basically a function of when they were installed. Semaphores were installed first and gradually were replaced with light or position light signals. Light signals were more versatile being able to display a "flashing" aspect.

 

Light signals with two or three vertical heads are also typically interlocking signals. They work the same way, you MUST stop at a red.

You must stop at a STOP indication. Just because some of the heads display red does not mean you have to stop.

 

Non-interlocking signals are basically "permissive", which means that, depending on the particular rules, you must typically stop at a red but then proceed at restricted speed.

 

This tends to confuse people in the EU and UK. There are two different signal aspects and indications. One is STOP and the other is STOP and PROCEED. They are not the same indication. They are different indications. Intermediate signals tend to display stop and proceed. Signals at control points tend to display stop.

 

Dave H.

[F-UnitMad]

That soft "whoooosh" noise you all just heard was the sound of all this going right over my head...

 

Mind'you, the same would be true of detailed explanations of UK signalling practise, which of course, also had variations according to Company, and then even after the 1948 Nationalisation, according to Region....

[JWB]

The other side of the coin is operating without signals, of course, and there are lots of options there. Modern short lines often just have an "operations manager" who drives around or keeps in touch with crews by cell phone. The crews know the routine and know when to keep out of each other's way. Small layouts would probably use this anyhow.

[BR60103]

CraigZ:

your signals book is pretty consistent with mine (Canadian, 1962 revision), but with the extra white signals added.

The rule numbers are different and the latest version has another set of numbers.

[signalmaintainer]

The other side of the coin is operating without signals, of course, and there are lots of options there.

 

One option to consider, one that I consider especially appealing for an otherwise "dark" model railroad, is the automatic interlocking, often found on an otherwise non-signaled section of railroad, such as where two competing lines cross at grade.

 

Automatic interlockings, as the name implies, are not under the control of a dispatcher or control operator. Rather, they operate under the "first-come, first-served" principle. A train encountering a red absolute signal at an automatic interlocking must stop short of the signal. A crewman walks over to the signal case, opens a small door on the side, and presses a button to request a cleared signal. The plant makes its checks and if all is OK, clears the signal for the requested route, locking the other signals to red, and the train can proceed.

 

Distant signals in approach to the plant provide an indication of what aspect the interlocker's absolute signals are displaying. If the absolute in advance is red, the distant's aspect will be yellow (indication: proceed prepared to stop at next signal; reduce speed to 30 mph).

 

In some cases, the owning (or superior) railroad's absolute signals always display something less restrictive than Stop (unless the plant is lined for a move by the inferior railroad). The superior railroad's distants could then display a green or flashing yellow. In this case, the inferior railroad's distants would be fixed at yellow, as their trains always have to stop at the interlocking.

 

I think I read somewhere that a nifty computer program is available to do all this. Or, you could build the vital circuitry yourself using about 25-30 relays! I've got a plan for the latter, if anyone's interested.

[dave1905]

CraigZ:

your signals book is pretty consistent with mine (Canadian, 1962 revision), but with the extra white signals added.

The rule numbers are different and the latest version has another set of numbers.

 

The white signals in the diagrams aren't white, they are shown as placeholders for the descriptions of the signs. The lights will be the colors of one of the aspects above.

 

There are signals that are "white". Technically the color of the "white" signals is "lunar" which is a bluish white, sorta the difference between the color of a regular headlight and a halogen headlight.

 

So if you read about a lunar signal, it isn't about NASA or space aliens. 8-)

[CraigZ]

The other side of the coin is operating without signals, of course, and there are lots of options there. Modern short lines often just have an "operations manager" who drives around or keeps in touch with crews by cell phone. The crews know the routine and know when to keep out of each other's way. Small layouts would probably use this anyhow.

 

I had the pleasure of operating on a New York, Ontario & Western layout located in Wisconsin that was 'dispatched' that way. The dispatcher walked around and gave clearance/permissions/etc as needed. Very purposeful operation but also very low key...I enjoyed it a great deal. I operate twice a month here on a layout with full signals, a CTC board, radios, etc...about 14 guys needed to operate it properly. And it's much more stressful...but still fun! FWIW it was in the July/Aug 1999 issue of Model Railroading...which is of course the only issue missing in the Trainlife index for that year...

 

 

 

[dave1905]

A critical thing to understand is that on single track ABS signals do not convey authority on the main track. That is, the signals by themselves do not allow the train to operate on the main track. They tell the train how to proceed and warn of track conditions ahead.

 

There is a system to grant authority on the main track,such as timetable, train orders, track warrants, DTC, OCS, Form D, etc. The ABS is overlaid on top of those systems.

 

Conversely, with CTC the signals actually convey authority to occupy the main track.

 

With ABS a clear signal doesn't necessarily mean the train can go. In ABS "stop" signal doesn't necessarily mean the train can't pass it (one of the reasons I think calling stop signals "absolute" creates more confusion than clarity).

 

With CTC a clear signal means the train can go and a stop signal means the train has to stop and can't pass without further authority.

[dave1905]

I had the pleasure of operating on a New York, Ontario & Western layout located in Wisconsin that was 'dispatched' that way. The dispatcher walked around and gave clearance/permissions/etc as needed. Very purposeful operation but also very low key...I enjoyed it a great deal. I operate twice a month here on a layout with full signals, a CTC board, radios, etc...about 14 guys needed to operate it properly. And it's much more stressful...but still fun!

 

I would consider the other operation much more stressful than the CTC. In CTC there is zero pressure on the crew. If the signal is clear they go, if its stop they stop, anything else they go slow. Very low pressure. You don't go anyplace unless the dispatcher gives you a signal.