CPL signals and how they operate

[NW Mailing List]

Abram, I guess we will have to disagree about whether speed signaling or route signaling is superior. While speed signaling provides more information, I much prefer route signaling as it avoids the need to slow down more than the track requires in order to conform with the speed required by the signal. I spent six years commuting in the Chicago area on the former Milwaukee Road which uses route signaling which IMHO, is a good thing as the MILW liked 40mph turnouts (they’re all either 40, 25, or 10). Trying to make that work with speed signaling, assuming Medium = 30 and Slow = 10, would me Medium Clear or Approach over a 40mph turnout and giving up an extra 10mph, Slow Clear or Approach over a 25mph turnout and also giving up 10mph), and I guess you could only use Restricting over the 10mph turnouts. Of course, you could define Medium speed to be 40 and slow to be 25 but you’d still have an issue with those 10mph crossovers.

Route signaling does require that the engineer be aware of the route (reading the track if needed) when there are multiple routes possible at different speeds. Unfortunately, and it caused loss of information, the Milwaukee used diverging signals at converging points (something the N&W did not) - by that I mean, at a junction where two tracks converged into one (and there was no diverging option at all), they’d still use a diverging signal on the inferior track even though a non-diverging signal was not possible. On my commute, there was a point where we’d always get Diverging Clear but there were two possible routes we might take depending on traffic - through a 10mph crossover from track 2 to track 3 and then around a 15mph curve or hold track 2 and then around the 15mph curve before converging with another line (the reason for the diverging signal). If the latter, you could hold the 70mph track speed an extra quarter-mile before needing to comply with the speed restriction. And, you guessed it, one morning, our engineer thought we were holding track 2 and took that 10mph crossover way too fast (that junction has subsequently been resignalled with the one interlocking split into three so that problem cannot no longer occur - but it would not have occurred if the Milwaukee had not used diverging signals at converging locations). BTW, for those who are familiar with the MILW, this was at A-5 (Pacific Jct.) which is now A-5, A-6, and B-6.

OTOH, at another location, Metra (as owner of the ex-MILW lines), expanded an interlocking (B-12) and ended up with some signals that needed to display a Diverging signal for both 25 and 40mph routes. At this one, they went with multiple aspects - Red over Green over Red for the 40mph routes and Red over Red over Green for the 25mph routes - and covered by at timetable special instruction (one of the more interesting things about these routes is Metra owns it, employs the train and engine crews for their trains, and even employs some of the tower and consolidated control center operators but CP officially dispatches it (from Minnesota) and it’s covered in a CP employee timetable).

To your second point, my note yesterday made reference to the non-standard signals we had at Sandusky. They had been left in that intermediate converted state mentioned last night by Rick Stone (no relation) - red for the horizontal, lunar (Rick called it yellow but I always thought they were lunar) for everything else. They were non-standard but not covered in the timetable. The rationale I was given is they were only seen by yard crews and everyone concerned knew what they meant.

-- 
Larry Stone
lstone19 at stonejongleux.com





> On Jan 23, 2020, at 4:12 PM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:
> 
> Comrade Cochranoff, Excellency:
> 
> Your read of the literature is spot-on, to use the current idiom.  Those code rates, 180-120-75, were just about the exclusive standards in the coded signal business.  With those 3 code rates, plus absence of code, almost anything that a railroad needed could be done for block signaling and cab signaling.  Which is probably the reason Union Switch & Signal marketed it under the name  **Universal Code.**
> 
> May I offer a couple small suggestions on a couple of small things ...?
> 
> FIRST:
> 
> Originally, the N&W did not use the word **Diverging** in its signaling, but instead used the name of the speed involved, either **Medium**  or  **Slow.**   The N&W used main track turnouts good for 30 MPH, which is called **Medium Speed** in the industry.  By contrast, another type of turnout is the one good for only 15 MPH, and 15 MPH in the trade is called **Slow Speed.**  These categories of Medium Speed and Slow Speed can even be seen in the N&W Rule Books in the days of semaphore signals.   (Beginning in the 1940s, some railroads with serious high-speed passenger demands, such as the NYC, introduced the 40Frt / 45Pass MPH turnout, and that speed was given the name **Limited Speed.**)
> 
> The N&W had a **Speed Signaling System** which told the engineman how fast he could move through a turnout:  Medium Speed, or Slow Speed.
> 
> The alternative system to Speed Signaling is **Route Signaling.**  A Route Signaling System is one which simply tells the Hog Head that he will be moving through a turnout, and it is up to him (and his Time Table) to figure out the permissible speed through that particular turnout.
> 
> So, if the N&W originally had the superior Speed Signaling System, what went wrong, that they ended up with only a Route Signaling System by the 1960s?  The answer is that the N&W merged with the NKP and the WAB, and both of those roads had only Route Signaling.  And someone in the decision making pecking order at Roanoke had to decide whether to publish the aspects of both types signal system in the combined Rule Book, or just to downgrade the N&W's Speed Signaling nomenclatures to those of a less sophisticated Route Signaling System, and have only one set of aspects in the Rule Book.
> 
> The decision was to go the latter way:  Make everything just a route signaling system.  And when the blue-covered Rule Book came out after the merger, that is what it contained.  I tried to find out who made this decision, but without results.  The only thing this meant on the On the N&W portion of the merged company this meant two changes:  (1) The names of the Aspects changed, and (2) the maximum allowable speed through all the main track turnouts had to be published in the Time Table Special Instructions.
>   
> 
> SECOND:  
> 
> The **conversion**  of Position Light Signal aspects to the so-called **CPL**  system was nothing more than the substitution of red and green glasses for the NoViol's in the appropriate places, and the removal of the Neutral (middle) lights on the top and bottom arms.  There was no need to change anything in the circuitry.  Which has always made me wonder why anyone would want to use the name Color Position Light Signal for what the N&W had,  when nothing changed but a few glass covers.  Earlier on, that term was used only in connection with the B&O's quite elegant (and very efficient) signal system designed by their Chief Signal Engineer, Frank Patenall.  But it is what it is and that cow is now long out of the barn...
> 
> As a final tid-bit on this issue, I will add that even after the signal names were changed to **Diverging**, many of the signals still had all NiViol glass, and none of the new green and red glass.  I believe the entire Scioto Valley Division (**Columbus District**) was this way for a long time after the blue Rule Book came out:  same old glass, new names for the signal aspects.  My guess is that the N&W quickly installed the colored glasses in Rule 261 territory (**CTC**) and on single track railroad, and left the double track Rule 251 ABS territory for later.
> 
> THIRD:
> 
> My guess is that the coded track signal system the N&W bought in the very late 1930s stayed in place until Electrocode started coming on the market in the mid-1980s.  What the N&W had in place was paid for, and there was nothing any better.  The benefit of Electrocode (and its related permutations, the names of which I cannot recall) was that it was solid state and worked not by currents, but by Radio Frequencies propagated through the rails.  The great expense of scientific-grade signal relays was eliminated, as was the maintenance of all pole line.  And because the impedance of steel rail to an RF is far, far lower than its impedance to AC currents or its resistance to DC currents, the length of blocks could be extended up to 4 miles before RF signal strength attenuated to the point where it was no longer usable, and cut sections could be eliminated.  An additional benefit is that the number of insulated joints in the track was drastically reduced because the RF's could be grounded off without putting an insulated break in the rail.  But the drawback has always been that electronic equipment is extremely sensitive to transient voltage spikes (such as lightening,) and you cannot fuse against it because the transient currents will run right through the fuse and zap the circuit board before the ground protection flashes over or the fuse wire melts.  The best you can do is install back-to-back Zenar diodes packaged together in a Transorb, but I have seen those things blown into tiny fragments by a lightening strike.
> 
> Hope this helps.  But here is the caveat again:  I was never a Signalman, so consult a professional for a more complete explanation.  My level of competence on the railroad was pushin' box cars around in the darkness...
> 
> And thanks for sending the 1940 article.  Attached is a photo of one of those (now rare) square-type code transmitters with a round window in front.  The little green ceramic package on top is a Transorb, but I use it for spark killing at the contacts, not for lightening protection. 
> 
> ------- abram burnett,
> dilettante in da turnip patch
> 
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