A blog devoted to explaining the ins and outs of North American railroad signaling, past, present and future. This blog seeks to preserve through photo documentation the great diversity and technical ingenuity of 20th century signaling and interlocking hardware and technology. Related topics cover interlocking towers and railroad communications infrastructure.
Note, due to a web hosting failure some of the photos and links may be unavailable.
This news isn't exactly new, but I figured I should go over the signaling implications of the end of Montana Rail Link's lease of 400 miles of former BN Main Line in the state of Montana.
Classic Northern Pacific Searchlit Cantilever Mast on MRL
MRL is fairly special in that it runs a high quality CTC main line with modern motive power such as SD70M-2's. Like many regional railroads with signaling, changing out its legacy equipment was never a high priority, especially since it was PTC exempt and the the physical plant was leased not owned. MRL's former Northern Pacific/Burlington Northern trackage is largely signaled with searchlights and GRS Type D color light signals with a mix of masts, small vintage gantries and cantilevers.
BN vintage GRS Type D masts on MRL
MRL was in the process of having many of its legacy signals replaced by BNSF standard Darth Vader types with relay box mast combos being a popular replacement choice. The reversion to BNSG is likely to accelerate the replacement process and although BNSF could in theory try and get a PTC exemption if it does not need to run TIH cargo on the line, provisions to make the route available for some potential passenger services make the prospect of government infrastructure money highly likely and with that comes a brand new bland signal system sooner rather than later.
Brand new BNSF type Darth Vader type signals newly installed on MRL.
As of this writing the lease termination appears to still be under review and if the limbo state accelerates and decelerates the existing re-signaling efforts remains to be seen. I recommend anyone in the area to get their photos now, the more the better.
Well it's time to cross the Mississippi and get this series finished up. Today I will be exploring the signs of the Western freight roads. Today this would be UP, BNSF, KCS, CP (former SOO) and CN (former IC).
We'll begin with the BNSF and you can't spell BNSF without ATSF. Spoiler, western railroads had a big thing for white signs and black lettering so most of this post is going to be discussing all the ways one can do a white sign with black lettering and in my opinion the ATSF did the best job with white signs on black letters by adding a black border to the signs and a somewhat distinctive font. In this photo below we can see an example on the BNSF Raton Sub showing a single interlocking with a free standing ATSF style sign (probably from late in the ATSF era in the 1990s, and then more plain black on white BNSF signage mounted on the relay hut.
Elsewhere on the Raton sub we see a non-black border sign with the same ATSF font.
And finally we have a BNSF standard font.
On the BN side of the house we see a similar style of free standing black on white sign using a two post support. On certain single track territories, interlocking signs would sometimes be replaced by a station sign similar to the one seen below.
In Europe, mechanical signaling is still quite common. Paired with the manual block system, all or nearly all-mechanical interlocking towers control thousands of miles of main line track. However in North America, the all-mechanical tower, that is with semaphore signals controlled directly by levers and pipeline, is virtually unheard of . Yes examples can be found at drawbridges and diamond crossings on low density track, but the difference is quite stark. Part of the reason is the general incompatibility of automatic block and mechanical signals. Manual block was much less popular in North American than in Europe. The other reason had to do with a number of ICC regulations that required signals to be interlocked with train detection (read track circuits) and that signals be electrically interlocked with point detectors.
You can imagine my surprise when I discovered Neilson Jct in Neilson, IL to have a set of fully mechanical signals controlling a manual block style junction with non-Restricted speed movements. Now RR Signal Pics does a great job providing basic details about Neilson, but I just wanted to not only call attention to that page, but also to a set of videos that have been on Youtube since 2011, but due to poor use of keywords, does not appear on most interlocking tower or signaling related searches.
For a single switch between two secondary tracks, Neilson has a surprising number of levers. First, just like in British practice, each former C&EI distant has its own lever. Second, each of the southbound signals are connected to derails which also come with a facing point lock. Finally, the 12 lever operated a mechanical timer that I assume provides approach locking in the absence of track circuits.
The northbound home signal handled the route route selection issue by having two semaphore heads, each controlled by a different lever and indicating one of the two routes. Of course the straight route semaphore was for the C&EI and the lower diverging route semaphore for the BN.
Aside from the British style of operation, what really puzzles me is how such a tower survived up through 1989. Checking Google Earth it appears the single junction switch was replaced by a hand operated type and that the line is un-signaled.
Basically just watch the 7 videos and read up on the RR
Signal Pix page. I'm just trying to call attention to an historical
oddity that is in need of some help with discoverability :-)
In 1996 the Burlington Northern Railway merged with the Atchison, Topeka and Santa Fe. Typically when two railroads are involved in a mega-merger the signaling systems are so incompatible that the surviving railroad needs to employ multiple signal aspect systems, or the systems are similar enough that they can be merged without much change. However when looking at the famous BNSF signal chart we see an almost bizarre mix of route and speed signaling, almost as if two different systems that should have been kept separate were merged. The shocking truth is that prior to the merger, both BN and ATSF used very similar bizarre signaling systems and the merger was nearly seamless.
Like I said, what stands out is the mix of route and speed signaling. At home signals it's all route with Diverging Clear and Diverging Approach. At the distant however we see Approach Medium and Approach Limited, traditionally speed signaling aspects. This is why it feels like one road was speed signaled and one was route signaled since it would be easy enough to just remove the speed signal aspects at interlockings and just rely on the timetable while applying speeds to the distant signals. However if one goes back and looks at the original ATSF and BN rules, we can see what actually happened.
BN Chart is a PDF so click the link.
Both these nominally route signaled western roads included speed signaling aspect Approach Medium and Approach Restricting while the ATSF additionally included Approach Limited . During the unification process BN's Approach Diverging was simply folded into Approach Medium so that the rule now reads "Approach next signal at Medium speed (40mph) AND prepared to proceed on diverging route". In practice the Y/Y is still used for diverging routes 40mph and below while *Y* tends to be used for 4-block signaling, however this was not always the case on legacy installations, which allowed for two lamp distant masts.
Approach Medium (Diverging)
Approach Medium (to Stop)
The other signal that stands out is the use of Y/G for Advance Approach. Now with the Y/Y Advance Approach popular in the east being used for Approach Diverging, it does make some sense to use Y/G, but why was *Y* labeled Approach Medium and then used in the role of of Advance Approach as seen in the preceding video? Well on BN this remains a bit of a misery, but from the ATSF side of the family tree we got what became the final BNSF rule that states pass next signal at 50mph AND be prepared to advance on diverging route. It's basically filling the role of Approach Limited, or in Union Pacific parlance, Approach Clear 50. As BNSF re-signals it appears to be common practice for distant signals to display Y/G Advance Approach for Diverging Clear in the 30-50mph range and Y/Y Approach Medium for Approach Diverging (or the extra block length gained with an interlocking allows for a more permissive 4-block signaling). However this could just be BNSF installing signal lamps that aren't used.
BNSF has been investing in 6 lamp distant signals that can display Y/G and Y/Y.
Now I know you must be looking at the signal chart and noticing that there is indeed an Approach Limited using Y/*G*. Well again, read the rule, not the name. It's basically the same as Advance Approach, only the speed is raised to 60mph for high speed turnouts. On UP this is more appropriately called "Approach Clear 60".
To make things even more confusing BNSF maintains a distinction between R/*Y* and R/Y/Y. Whereas R/*Y* is typically used for back-to-back diverging movements, on BNSF it is labeled Diverging Approach Medium and is clearly intended for short signaling distances as there is no mention of proceeding on a diverging route and the speed is limited to 35mph instead of 40. R/Y/Y is the more straightforward Diverging Approach Diverging, but appears on neither of the predecessor systems so as one might guess R/*Y* is still used for back to back diverging movements where BN traditionalists still hold sway. I have to assume the R/*Y* Diverging Approach indications on the ATSF were converted to plain R/Y.
Diverging to stop at the second signal over Diverging Approach Medium
While BNSF allows for both Lunar white and *R* Restricting, the *R* is clearly the preferred choice nowadays. Like UP, BNSF only employs Y/L for Approach Restricting without the obvious Y/*R* option. However unlike UP there seems no desire to distinguish Yard routes with Lunar and occupied block routes with *R* as I have not encountered any 4-lamp signal heads. (For those who don't know, Approach Restricting provides advanced notice of being routed into a yard or non-signaled siding).
So there are the interesting parts of the BNSF signal aspect system. Hopefully I'll get some feedback regarding how some of the overlapping indications are utilized out in the field and also some more of the historical context I'm not aware of. Specifically I was unable to locate either a CBQ or GN signal aspect chart to trace to origin of the odd speed signaling components further.
