Modeling C&O CTC--Part 1: The basics

In fond memory of Stewart H. Bostic The finest signalman I will ever know

The series of articles debuting in this issue is intended to give a better understanding of how the C&O's signal systems operated, and how to apply these principles on a C&O-inspired model railroad. Among the topics to be discussed over the course of the series are proper location of signals, the requirements for clearing a signal at an interlocking, how to model a CTC control machine, proper use of signal aspects and indications, and how to model the prototype signals themselves. The practices discussed in this series reflect C&O practice from about 1940 to 1968.

I have had an interest in railroading, and in railway signal systems, since I was about ten years old. I always enjoyed wiring my Lionel layout and in later years my HO scale layout. It was this interest that led me to write the C&O Historical Society for information on C&O signal systems.

The Society put me in touch with Stewart H. Bostic. Stewart worked for the C&O from 1944 to 1985, at which time he retired as Supervisor of Signals and Communications at Clifton Forge, Virginia. Stewart took the time to teach me the art of signaling through many long telephone calls and letters. His patience in trying to teach a young man not yet out of high school was the greatest gift one could ever receive. It was with his encouragement and willingness to teach me that I was able to learn the necessary skills that I put to use today in my job as a signal maintainer for the Canadian National Railway in Pontiac, Michigan.

Model railroading is still my hobby. I try to spend as much time as possible working on my models and doing research for, as I like to call it, "The Dream Layout." I don't yet have a layout, but work on buildings and locomotives. I plan to model the C&O's James River Subdivision from Clifton Forge to Gladstone, Virginia, circa 1963 to 1965. I am currently helping my friend Chuck Liford who models Conrail's Indianapolis Line from Berea, Ohio, to Indianapolis. While it's not the C&O, as I jokingly remind him when things go wrong, I enjoy working on it all the same. I have recently completed the Centralized Traffic Control (CTC) system on his entire main line.

There are many books available that give a good description of how railroad signal systems work. One title in particular that comes to mind is Railroad Operation and Railway Signaling by Edmund J. Phillips. Like all the books I have found on this subject, however, it gives general descriptions of standard practices used throughout the railroad industry, and does not focus on one particular prototype. Each railroad applied the standard practices in its own unique way, and the C&O was no exception.

It is important to note that the practices to be discussed in this series do not reflect the Pere Marquette District. The C&O's signal engineering was done in Richmond and, in later years, Huntington. The PM District's was done in Detroit, and although similar, the PM District's practice did vary from the rest of the C&O system. CTC, and signaling in general, is an involved subject that I will try to keep simple, without omitting any important points.

An early signal engineer once said, "The art of signaling may be quite truly termed the art of saving seconds safety." One could say that the C&O embraced this idea, purchasing CTC for much of its main line. Beginning in the mid-1930s the C&O continued construction from one division to another as time and money became available. The priorities were established according to traffic density and savings. On average, CTC saved trains 42 seconds per mile and permitted passenger trains to make up lost time without delaying other trains. Compared to timetable and train order operations this was a vast improvement, not to mention CTC greatly reduced the chance of human error. The economics alone of eliminating telegraph offices and interlocking operators made it justifiable for the C&O to install CTC.

CTC is defined as "a block system under which train movements are authorized by block signals whose indications supersede the superiority of trains for both opposing and following movements on the same track." CTC provides centralized control for signals and switches within a territory of defined limits, controlled from a single control console known as a control machine. Because the distance between the control machine and the field locations in CTC territory usually extends a number of miles, the system is controlled by code and carrier equipment. A direct-wired arrangement would require one pair of wires for each controlled signal and switch within the CTC territory, and would not be economical. The code-and-carrier system allows the CTC system to operate over only two line wires, known as the code line. This circuit is the most important pair of wires on the pole line-moreso than the dispatcher's phone circuit and is the first to be repaired if major damage to the pole line occurs. The control machine provides a means for the dispatcher to monitor wayside conditions and to initiate the control codes through push buttons and levers. The control codes are sent to the field equipment via the code line to control the corresponding signals and switches.

Each end of a siding controlled by the dispatcher is called an interlocking. In contemporary railroading this is called a control point (CP). The definition of an interlocking is: "An arrangement of signals and signal appliances so interconnected that their movement must succeed each other in proper sequence and for which interlocking rules apply." Each signal governing entrance to an interlocking is called an interlocking signal or home signal. These signals display stop (rule 292) as their most restrictive indication. When a less-restrictive indication than "stop" is displayed, a signal is said to be "cleared." The track between the outer opposing signals is referred to as the interlocking limits. The detection circuit (track circuit) within the interlocking limits is known as the detector track circuit. The dispatcher calls this same circuit the O.S. section, O.S. meaning "on sheet." When this circuit becomes occupied by a train the dispatcher will show on his train sheet that this train is by the location that corresponds with that particular circuit.

Not all signals in CTC territory are controlled by the dispatcher. Intermediate signals (signals with number plates) generally govern movements between interlockings and are commonly spaced at one train length apart. These signals are usually operated automatically within the CTC system and their aspect determined by train location and track condition. Signals controlled by the dispatcher do not have number plates and are two or three unit signals. Each signal unit was commonly referred to on the C&O as an arm. This comes from the early days when the blade on a semaphore signal was called an arm. Each signal unit may display one, two, or three colors. Some people call each color in a signal unit an aspect; but do not be confused: an aspect is the appearance of a signal conveying an indication either by one color being displayed or by a combination of colors being displayed. Each color is correctly referred to as a light. Signal units that display only one color are called marker lights.

Signals in CTC territory controlled by the dispatcher have the prefix on the control machine "L" or "R." This comes from the days when the operators were located in cabins along the tracks. As might be imagined, L signals were to his left and R signals were to his right. When the C&O began installing CTC, L signals became westbound and R signals became eastbound. All tracks in the C&O timetable are listed as east and west even though they may geographically run north and south. In the event that the tracks do run north and south, north becomes west and south becomes east. In conjunction with the L or R prefix signals are numbered evenly, 2, 4, 6, 8, etc. For example, a westbound signal at the east end of the siding could be labeled L88. The eastbound signal would be R88. Switches and electric locks are labeled with odd numbers-1, 3, 5, 7, etc.-so the switch at the east end of the siding would be 87. The numbering sequence usually started at a low number at the west end of the territory and would get higher as you moved east, however the numbering sequence did not continue consecutively. As shown in Figure 1, the west end of the siding is signal L and R82 while the east end is L and R88. This allows for possible expansion. For example, if we wanted to add a crossover in the middle of the siding between the east and west ends we are able to use L and R84 and switch 83 or L and R86 and switch 85.

Power switches operated by either electricity or air are labeled on the control machine N and R for normal and reverse-- normal being the main track route and reverse being the diverging route, either from one main track to another or from the main track to a siding. Electrically locked switches are also labeled N and R for normal and reverse-normal being locked for the main track and reverse being unlocked and the switch lined for the siding. An electric lock provides a means of locking a manually operated switch with the signal system so that the switch cannot be operated unless traffic conditions permit.

Figure 1 shows a standard layout of signals at both the east and west ends of an interlocked siding in CTC territory. The dispatcher controls all signals and switches at this type of location-Figure 2 (p. 24) shows the standard arrangement of signal units. Home signal 8174 governs eastward movements over the power switch in the facing-- point direction, either across the main track or into the siding. This signal is known as a "facing-point" signal. The top or (A) unit has three colors; red, yellow, and green. This unit governs eastward main track movements through the interlocking and to the next governing signal. The lower or (B) unit has two colors; yellow and red. This unit governs eastward movements through the interlocking from the main track into the siding. Home signals L 174 and LC 174 govern westward movements over the power switch in the trailing-point direction, and both are referred to as "trailing-point" signals. Both signals govern westward movements through the interlocking and to the next governing signal. Signal L174 governs this movement across the main track. The (A) unit of this signal is again a three-color unit; red, yellow, and green. Like 8174, it also governs main track movements, but in the westward direction. The (B) unit is a red marker light that identifies this signal as a home signal. Signal LC174 governs the trailing-point movement from the siding to the main track. This signal is of the dwarf type. A dwarf signal is a low signal used in yards or at a siding or where clearance restricts the use of a high signal. This signal also has three colors; yellow, green, and red. Both ends of the siding would have the identical arrangement of signal units, but using the next couple of numbers higher in the sequence. The prefixes L and R are also reversed to show the proper direction at that location.

Part Two

The next installment of this series will discuss the requirements for clearing a signal at an interlocking.

Acknowledgments

I would like to thank Todd Miller, Justin Tiller, Tom Dixon, Margaret Whittington, Chris Wiley, Russ Hass, Kevin Holland, and David Hilton for their assistance in the preparation of this series of articles.

Copyright Chesapeake and Ohio Historical Society, Inc. Jan/Feb 2002
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