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Monday, July 17, 2017

Come and 'C'

In the 1940's someone at the always cost conscious Pennsylvania Railroad wondered why if signals could be displayed in the cab, why was there any need to display them on physical wayside signals? Although not the first railroad to have such an idea, the PRR was the first to at least make such a concept ready for prime time. Implemented on the important-yet-not-that-important Conemaugh Line between Kitski and Conpit Junction, the PRR's main innovation was the 'C' Board or "Clear to Next Interlocking" signal, which allowed trains with failed or inoperative cab signals to proceed to the next fixed (and presumably absolute) signal, while still technically operating under signal indication and thus not needing to receive some sort of written movement authority. The assigned rule number, 280a, actually betrays the concept's roots in the old Manual Block System Rule 280, Clear Block, as opposed to Rule 281 Clear used in automatic signaled territory. Still numbered 280a under current NORAC signal rules, this can now be considered an Artifact Title since Rule 280 was long since removed. Both 280 and 280a can be lumped into the class of "super clear" indications, that can give trains 10 or even 20 miles of railroad at a shot.

Now I'd love to talk about how the technology behind Rule 280a works and how displaying 280a was implemented in towers, but both of those topics are the subject of ongoing research. Instead, today's post will focus on the 'C' signals themselves and how they evolved from the PRR's first deployment on the Conemaugh Line, through to the current flood of "Rule 562" territory on both Amtrak and Norfolk Southern.

The PRR's inaugural style of 'C' lamp was very much an ad hoc affair, making use of whatever materials were at hand. The the flashing lunar white marker lamps were provided by US&S PL-3 units, common to PRR position light signals, and they were surrounded by a rectangular piece of sheet metal with a white 'C' painted on it. The unit was attached to a standard PL mast by means of steel tubes that looked a lot like the type used to mount PL units to the central hub on PRR PL high signals. Here we see a surviving example of this type of 'C' lamp installed at CP-CONPIT.

Almost 50 years would pass until this method of operation once again gained traction. Metro North was looking to replace the New Haven vintage suspended semaphore signals, but the layout of the electrification system would either require completely new signal bridges or new suspended signals that would come with many of the same maintenance headaches. The solution was 562 operation that would allow most wayside signaling locations to be just removed from service. As 1980's Metro-North was still somewhat rooted in Conrail operating rules, it adopted the 'C' signal making use of PL-3 units surrounded by a pill shaped backing with a white 'C' painted above the lamp.

Conrail was next to pick up on the cab-signal-only crazy as a number of its cab signaled former PRR routes came up for re-signaling. The Morrisville Line, formerly the PRR Trenton Cutoff, made use of GRS SA searchlight heads modified to display a single lunar white light with a small reflective white 'C' on a flap of sheet metal mounted above. I am not sure if Conrail was recycling surplus SA heads made available in its transition to tri-light signals or if they were purchased new.

The next generation of Conrail "562" followed shortly thereafter with installations on the Fort Wayne Line and the east end of the Boston Line between Framingham and Worcester. These made use of more traditional railroad marker signal lamps, each mounted with a circular backing and the same metal 'C' flap as seen on the searchlights.

 Of course one must account for dwarf signals. In both the Safetran stack and searchlight configuration, Conrail would place an extra lunar white Safetrain cube signal to the right of the signal with the same reflectorized metal 'C' fmap. On the Morrisville Line, there was at least one instance of PRR PL dwarfs getting an attached 'C' lamp, but these were replaced a number of years ago.

Meanwhile, the MBTA was the next railroad to employ 'C' signals when it rebuilt its Old Colony Lines. Here the distinctive feature was the reduced size of the 'C' lamp target, looking a bit like one of those small round lollipops. Like with Metro-North, the 'C' was incorporated into the target, placed above the lamp, which itself was of the Safetran square modular variety. 


Fast forward to the 2000's and, like everything else signaling related, it appears that the venerable 'C' lamp has been standardized. Starting with Amtrak's 1999 Secaucas Junction and high density signaling project, Rule 280a has been displayed by a pair of Safetran modules, the lower one holding the flashing lunar white lamp, and the other one a reflective (or possible backlit) 'C'. This in turn is surrounded by a pill shaped backing, similar to the original Metro-North style. This layout has gone on from Amtrak to be employed by New Jersey Transit and Norfolk Southern.

The one exception is in the realm of dwarf signals where Amtrak's standard modular LED searchlight was modified to mount a lunar LED lamp next to the lower "head" of the dwarf stack and a blanked module with a white 'C' next to the upper "head" of the dwarf stack.  BTW, anyone wondering what a 'C' light looks like when displayed, here you go.

Will there be more varieties of the 'C' signal?  Possibly.  There are a lot of railroads with a lot of signaling systems that haven't yet done all in with the waysideless future.  What happens they are certainly more interesting than plan old Darth Vaders.


  1. Is the signal in the video back to back with another interlocking? Otherwise how can you get clear to next block and still get approach?

    1. Sometimes railroads do that. Sometimes it's justified by high density blocks, sometimes I assume it's just to make things uniform. 🤷‍♂️