Trains.com

Signaling nomenclature

2119 views
24 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    March 2016
  • From: Burbank IL (near Clearing)
  • 12,565 posts
Posted by CSSHEGEWISCH on Saturday, September 25, 2021 10:02 AM

I remember that picture, it was in TRAINS.  The bridge involved was the K&IT bridge over the Ohio River at Louisville.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
  • Member since
    March 2003
  • From: Central Iowa
  • 6,035 posts
Posted by jeffhergert on Friday, September 24, 2021 8:07 PM

CShaveRR

The railroad drawbridge along Interstate 55 in Chicago (over Bubbly Creek...you don't want to know!) had absolute signals protecting it at either end with four heads.  Somewhere I should have what those indications were.  It involved the fact that three railroad lines (ATSF, GM&O, and IC) converged to cross this two-track bridge, then diverged again on the other side.

 

I remember seeing a picture years ago, either in Trains or Railroad Magazine, of a multi-head signal where multiple railroads converged.  There was a plate for each signal head with the intials of the railroad it governed.

Could it have been for this bridge?

Jeff 

  • Member since
    October 2008
  • From: Canada
  • 1,600 posts
Posted by cv_acr on Friday, September 24, 2021 11:36 AM

SD70Dude
In Canada the offset and single aspect signals normally cannot display "stop" (there is an exception for a single aspect signal with a letter "A" plate, though I've never seen one on CN).  A solid red indication on these signals means "stop and proceed", or far more commonly "restricting" if the signal has a letter "R" plate, again, I've never seen one of these signals without an "R" plate on my territory. 

See CROR 436, 437 and 439:

https://tc.canada.ca/en/rail-transportation/rules/canadian-rail-operating-rules/general-description-location-fixed-signals

I have seen (and this is the only place I have seen) the "A" plate on the [main track] signals leaving sidings on ABS (not CTC) sections of Canadian Pacific's track through southern Ontario. Single head with "A" plate. Controlled CTC/Interlocking signals are always at least 2-head (vertically aligned) signals. Even if the bottom head is a "dummy" always-red light.

CN's track around here all full CTC (or completely unsignalled branches/spurs), not ABS.

The "number plate" = permissive rule is common on US railways, but does not apply in Canada, this is where different rule books can trip you up on subtleties. Canadian rulebooks distinquish "Stop" and "Stop and Proceed" by the vertical/staggered alignment of the heads; this is not necessarily present in US rulebooks.

  • Member since
    October 2008
  • From: Canada
  • 1,600 posts
Posted by cv_acr on Friday, September 24, 2021 11:27 AM

CShaveRR

The railroad drawbridge along Interstate 55 in Chicago (over Bubbly Creek...you don't want to know!) had absolute signals protecting it at either end with four heads.  Somewhere I should have what those indications were.  It involved the fact that three railroad lines (ATSF, GM&O, and IC) converged to cross this two-track bridge, then diverged again on the other side.

 

Certainly non standard; descriptions of the particulars would have to be in a rulebook or TT special instructions somewhere.

  • Member since
    October 2008
  • From: Canada
  • 1,600 posts
Posted by cv_acr on Friday, September 24, 2021 11:25 AM

Someone equated "head" with "aspect" above; that's not quite correct. A single head signal has (usually) three aspects: Red, Yellow, and Green.

Signal glossary:

Signal - the whole thing (i.e. all of the lights on a single mast). Each signal applies to one track and one track only.

Head (also Target, although that can also just be the black metal disc around the head) - each individual light set (colour light) or blade (semaphore) on the signal mast. Each head displays one 

Aspect - the particular colour(s) the signal is currently displaying (e.g. red over yellow)

Indication -  the name/meaning of the aspect (e.g. "Approach"). Each aspect translates to a single Indication. An indication can be given by different aspects (e.g. Green aspect on a single-head signal, or Green over Red over Red aspect on a three-head signal are both "Clear" indication)

Bridge - a structure over the tracks that supports multiple signals (for multiple tracks).

  • Member since
    March 2016
  • From: Burbank IL (near Clearing)
  • 12,565 posts
Posted by CSSHEGEWISCH on Saturday, September 18, 2021 10:10 AM

blue streak 1

Bubbly Creek ?  anything to do with a witches' brew in the creek ?

All Chicagoans know about Bubbly Creek, it had its source within the Union Stock Yards.  The waste from carcasses from the various meatpacking plants was dumped into the creek.  As it decomposed and decayed, gas bubbles would form and rise to the surface.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
  • Member since
    December 2007
  • From: Georgia USA SW of Atlanta
  • 10,529 posts
Posted by blue streak 1 on Friday, September 17, 2021 8:57 PM

Bubbly Creek ?  anything to do with a witches' brew in the creek ?

Maybe each of the three bottom heads would be individually for routing on one of the various RRs ?

EDIT  Cannot even imagine the different number of aspects that could be possible especially with NYC's 2 aspect signaling ?

  • Member since
    June 2001
  • From: Lombard (west of Chicago), Illinois
  • 13,669 posts
Posted by CShaveRR on Friday, September 17, 2021 8:29 PM

The railroad drawbridge along Interstate 55 in Chicago (over Bubbly Creek...you don't want to know!) had absolute signals protecting it at either end with four heads.  Somewhere I should have what those indications were.  It involved the fact that three railroad lines (ATSF, GM&O, and IC) converged to cross this two-track bridge, then diverged again on the other side.

Carl

Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)

CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)

  • Member since
    December 2007
  • From: Georgia USA SW of Atlanta
  • 10,529 posts
Posted by blue streak 1 on Friday, September 17, 2021 8:22 PM

I have a failing memory.  However I remember traveling west along what was the NYC track in Indianna near Chicago.  At a very large lift bridge there was a signal that had 4 seperate heads.  All 4 did show red.  Fault memory or what ?

  • Member since
    February 2005
  • 2,037 posts
Posted by timz on Friday, September 17, 2021 4:48 PM

In the old days in the US -- a few decades ago, say -- single-head signals often did show absolute stop. If it was red, with no numberplate, it meant stop and stay. If it was red, with a numberplate, it meant stop, then proceed at restricted speed.

Dunno how common single-head absolute signals are now, but I doubt that they're rare in the US.

  • Member since
    December 2017
  • From: I've been everywhere, man
  • 3,688 posts
Posted by SD70Dude on Friday, September 17, 2021 4:17 PM

In Canada the offset and single aspect signals normally cannot display "stop" (there is an exception for a single aspect signal with a letter "A" plate, though I've never seen one on CN).  A solid red indication on these signals means "stop and proceed", or far more commonly "restricting" if the signal has a letter "R" plate, again, I've never seen one of these signals without an "R" plate on my territory. 

See CROR 436, 437 and 439:

https://tc.canada.ca/en/rail-transportation/rules/canadian-rail-operating-rules/general-description-location-fixed-signals

In the CTC territory I work single aspect and offset signals are always intermediate block signals that are not directly controlled by the RTC, I've never seen one at a controlled location.  Controlled signals are always non-offset two or three aspects. 

Things may be different in other areas or on other railroads. 

Greetings from Alberta

-an Articulate Malcontent

  • Member since
    February 2005
  • 2,037 posts
Posted by timz on Friday, September 17, 2021 4:08 PM

A hundred years ago, semaphore signals in the US could be upper-quadrant or lower-quadrant, which means what it sounds like: an upper-quadrant blade would be horizontal for stop and would turn 90 degrees upward to show a clear signal, and a lower-quadrant blade would be horizontal for stop and would turn downward to show clear. (Usually 60 degrees, but rarely 90 degrees.)

The difference was, upper-quad blades could have three positions -- horizontal, vertical and 45 degrees. Lower-quad blades almost never did that: the blade could be horizontal, or tilted 60 degrees down. No in-between.

So how would a lower-quad signal show the equivalent of a yellow light -- no need to stop, but plan to stop at the next signal? It needs two blades. That was the usual on many RRs circa 1910, before upper-quad semaphores became common. It was still the usual on SP and UP in 1940 - 1950; SP still had lots of two-blade semaphores in the early 1980s.

When you look at a pic of an SP two-blade semaphore -- there are lots of pics out there -- you'll notice the two blades are almost always different, indicating their different meanings.

https://www.flickr.com/photos/barrigerlibrary/12352960923/sizes/k/

(In that pic, the upper blade has started to drop -- he took the pic from the tail end of his train. Note milepost 589; he's at the east end of Garnet.)

Here's a NY Central rulebook -- it shows lower-quad and upper-quad aspects starting on page 80.

https://wx4.org/to/foam/maps/1rule/books/1918-10-30NYC-USRA_rules.pdf

  • Member since
    December 2001
  • 892 posts
Posted by mvlandsw on Friday, September 17, 2021 2:05 PM

On the Pittsburgh & Lake Erie the offset signals indicated that the next signal was an absolute signal.

Two and three blade semaphore signals were common before searchlight signals,  color position light signals, or other types replaced them.

  • Member since
    September 2003
  • 17,970 posts
Posted by Overmod on Friday, September 17, 2021 9:24 AM

tree68
If I recall correctly, some railroads differentiated between heads (searchlights) in line vertically and offset (one on either side of the mast).  I don't remember what the distinction was.

IIRC a road that did this was New York Central.  The differentiation was freight and passenger on that particular track.

  • Member since
    March 2003
  • From: Central Iowa
  • 6,035 posts
Posted by jeffhergert on Friday, September 17, 2021 9:01 AM

tree68

 

 
 

If I recall correctly, some railroads differentiated between heads (searchlights) in line vertically and offset (one on either side of the mast).  I don't remember what the distinction was.

 

 

IIRC, the signals that had the signal heads "offset" were permissive.  That is a train could pass them after stopping.  Signals with the heads "in line" were absolute.  A train couldn't pass an all red signal without further authority from whomever controlled the signal. 

The verticle distance between the signal heads also could change the meaning of a signal.  After some of these practices fell out of favor, rule books would carry the note that the physical make up of a signal (offset/in line, etc,) did not affect the indication of the signal.

Jeff

 

  • Member since
    December 2001
  • From: Northern New York
  • 22,573 posts
Posted by tree68 on Friday, September 17, 2021 7:18 AM

Lithonia Operator

So ...

In the US, a mast with three light heads on it constitutes one signal?

As already noted, yes.

It is the combination of colors in that stack of three (or two) that conveys the information.  Books have been written on the subject, and there are variations between railroads as well.  That was the cause of a rear-end collision near Chicago some years ago involving Amtrak.  The engineer read the signal correctly - but for a different railroad.  In that case he should have read it as a more restrictive aspect.

If I recall correctly, some railroads differentiated between heads (searchlights) in line vertically and offset (one on either side of the mast).  I don't remember what the distinction was.

B&O's color position lights (and similar systems on PRR, N&W, etc) are a different animal, although once you get the basics down, they aren't bad.  

LarryWhistling
Resident Microferroequinologist (at least at my house) 
Everyone goes home; Safety begins with you
My Opinion. Standard Disclaimers Apply. No Expiration Date
Come ride the rails with me!
There's one thing about humility - the moment you think you've got it, you've lost it...

  • Member since
    December 2017
  • 2,388 posts
Posted by Lithonia Operator on Friday, September 17, 2021 3:56 AM

Thank you, gentlemen.

Still in training.


  • Member since
    December 2001
  • From: Denver / La Junta
  • 10,296 posts
Posted by mudchicken on Thursday, September 16, 2021 11:19 PM

Mudchicken Nothing is worth taking the risk of losing a life over. Come home tonight in the same condition that you left home this morning in. Safety begins with ME.... cinscocom-west
  • Member since
    December 2017
  • From: I've been everywhere, man
  • 3,688 posts
Posted by SD70Dude on Thursday, September 16, 2021 11:13 PM

Yes.  Here are a couple examples (both photos by Brian Solomon).

One signal with three aspects/heads:

 

Two signals, each with three aspects/heads:

Greetings from Alberta

-an Articulate Malcontent

  • Member since
    December 2017
  • 2,388 posts
Posted by Lithonia Operator on Thursday, September 16, 2021 10:57 PM

So ...

In the US, a mast with three light heads on it constitutes one signal?

Still in training.


  • Member since
    May 2003
  • From: US
  • 21,491 posts
Posted by BaltACD on Thursday, September 16, 2021 10:20 PM

jeffhergert
When talking about signals, we usually are talking about block or interlocking signals.  But MC is correct that the term "signal" encompasses more than that.  Anything that conveys information affecting the movement of trains or engines is a signal.

Jeff  

Whistle Posts, Speed Signs (both temporary & permanent), Work Zone signs are all 'Signals'. 

  • Member since
    March 2003
  • From: Central Iowa
  • 6,035 posts
Posted by jeffhergert on Thursday, September 16, 2021 8:19 PM

When talking about signals, we usually are talking about block or interlocking signals.  But MC is correct that the term "signal" encompasses more than that.  Anything that conveys information affecting the movement of trains or engines is a signal.

Jeff  

  • Member since
    December 2001
  • From: Denver / La Junta
  • 10,296 posts
Posted by mudchicken on Thursday, September 16, 2021 7:12 PM

(A signal can be a light, a semaphore, a flag or a hand/motion indication)

Mudchicken Nothing is worth taking the risk of losing a life over. Come home tonight in the same condition that you left home this morning in. Safety begins with ME.... cinscocom-west
  • Member since
    December 2017
  • From: I've been everywhere, man
  • 3,688 posts
Posted by SD70Dude on Thursday, September 16, 2021 7:02 PM

A signal is each complete indicator for a track.  If we had a overhead bridge in double track territory it would have two signals on it, one for each track.  

The CROR uses both "head" and "aspect" to refer to each individual light on a signal.  We don't have any semaphores left and to my knowledge Canada never had any position light signals.  

The terms used may vary between railroads and rulebooks, just like the meaning of signal indications.

For example, in the CROR a single aspect signal displaying a flashing yellow indication is "Advance Clear to Stop", and it means that the next signal will be displaying "Clear to Stop" (solid yellow on top, with any lower aspects red) and the train must be prepared to stop at the second signal. 

On BNSF this same indication is called "Approach Medium", and it means that the train must approach the next signal at no more than 40 mph and be prepared to enter a diverging route.

Greetings from Alberta

-an Articulate Malcontent

  • Member since
    December 2017
  • 2,388 posts
Signaling nomenclature
Posted by Lithonia Operator on Thursday, September 16, 2021 5:18 PM

When a railroader refers to "a signal," is he talking about the mast and everything on it, in aggregate?

Or is "a signal" the name for each appliance on the mast? So, is a mast with three semaphores on it "a mast with three signals on it."

I ask because I've seen mention of a "three-blade semaphore." And I've certainly never seen a single appliance with three different blades; nor can I imagine how such a beast would be used.

Is the terminology standardized?

Is a mast with three searchlight heads a signal? Or three signals?

Still in training.


Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

Search the Community

Newsletter Sign-Up

By signing up you may also receive occasional reader surveys and special offers from Trains magazine.Please view our privacy policy