Interlocking Tower Audio Recordings

I've featured the work of the Youtube channel Railroad Media Archives before, but in the last few weeks they have taken a page from Evan Doobell's playbook with interlocking tower audio recordings from the 1960's and 70's. As you might be aware, the ability to capture long duration video information lagged the ability to capture long duration audio information by something like 5 decades. This means that recordings of interlocking tower operations in an audio/video format wasn't really feasible until the late 1970's, at which point everyone's favorite flags had fallen and conglomerates like Conrail and Amtrak were large and in charge.  While a great deal of vintage signaling technology was in use up through the 80's, 90's and Today, radio was well established along with its attendant operating practices such as track warrant control. 

Anyway,  Railroad Media Archives has so far posted three of these tower audio recordings covering HEATH and SUMMIT towers on the joint PRR-B&O C&N (Columbus & Newark) Railroad in Central Ohio as well as HIGH ST and MOUNDS towers in Columbus, OH. 

Hopefully we'll get to hear more of these sorts of recordings. They can certainly come in handy for any time one might be otherwise inclined to listen to radio.

The Sounds of Non-PRR Signaling

So I was about to post a second volume of PRR Signaling Sounds to highlight the importance of preserving both audio and visual history, but then I realized that I had a couple of non-PRR clips sitting on the back burner that deserved to see the light of day.



The first two were captured at some former Boston and Maine intermediate signal locations (BM mileposts 162 and 150) on the current Guilford Rail System Freight Main Line.  To the untrained ear they might sound a lot like the PRR signaling sound samples of cab signal code generators, and you would be right.  However why would cab signal code generators be used on non-cab signaled territory?  Well while the trains might not have been equipped with cab signal apparatus, the signaling department would use the 75, 120 and 180ppm codes sent through the rails as way to replace signal state wires on wayside poles.

When a signal location "heard" an Approach from the location ahead, it would know to display an Approach and transmit Clear.  When it "heard an approach medium it would display approach medium and transmit Clear and when it "heard" a clear it would display Clear and transmit Clear.  Hearing nothing would of course mean to display Stop and Proceed and transmit Approach. Later this technique would be updated with audio frequency signals instead of pulses of power frequency current, but at the time it was a clever way to use catalogue parts to eliminate costly pole lines.



Next we have a flashing Approach Limited signal at the 1950's vintage CP-LAUREL on the former Reading railroad Belt Line extension. A visit to the relay cabinet reveals a sound pulsing in rhythm to the flash of the signal, which of course indicates of an electro-mechanical flashing relay.  nothing super fancy, but it is a lot more reliable than what one might have to blink their Christmas lights on and off.  

Well, that's the extent of the non-PRR signaling sounds I have collected.  Don't worry all your PRR fans.  I'll be back soon with a second volume ;-)

The Sounds of PRR Signaling

This topic has come up a few times in other articles, but one of the neat things about non-solid state signaling technologies are the sounds.  Relays click, air hisses, motor generators....motor-generate?  One of the things I try to do on my documentary trips is capture any interesting sounds that might be escaping from one of the old relay huts or air plants.  My digital camera takes video just as well as stills so it doesn't take much extra effort and I then assemble the results into compilation videos for YouTube.

The following videos were taken mostly along the PRR Main Line or some of its connecting branches.  The sounds can be broken down into the following categories.

Air Hiss: Where switch points are operated by air, there is always a hissing leak somewhere.  Always.

Compressor Chug: When the pressure gets low enough, a compressor trips on.

Something Turning: Motor generators  or flashing relays typically have rotating parts.  When they get worn out, you can hear them.

Cab Signal Code Generators:  The most common sound I capture, electro-mechanical CSS generators generate pulses of current between 1 and 3 times a second. Code rates are 70 pulses per minute for Approach, 120ppm for Approach Medium and 180ppm for Clear. Generators are typically only active when code is being supplied.

The sounds are pretty self explanatory so I won't go into much detail.  Part of the fun is trying to determine which cab signal codes you can hear or what that rotating thing is doing inside the relay cabinet.

In the first video we have sounds from:

MP 53.1 signal on the Enola Branch in Cly, PA
CP-JEB on the Royalton Branch
ALTO interlocking in Altoona, PA
CP-SLOPE in Altoona, PA
MP 277 automatic signals at Fostoria, PA.



In the second video we have sounds from:

CP-PORT in Newport, PA
MP 131 automatic signals
MP 142 automatic signals
CP-MIFFLIN in Mifflin, PA
CP-HAWSTONE near Lewistown, PA



Anf finally in the third video we have:

MP 124 automatic signals
MP 196 automatic signals
HOLMES Interlocking, Holmesburg, PA



As you can see, "noisy" signaling components were installed up through the 1980's, but since then there was been a pretty much wholesale move to solid state.  After all, pulsing current is pretty much the hallmark of of what semiconductors can do :-\