Modeling C&O CTC

Part 4: Signal Aspects and Indications

Aspects and indications are the basic building blocks of the signal system. "Aspects" are the means by which the signal conveys its indication to the train crew, either by one color being displayed or by a combination of colors being displayed. The "indication" is the action that the aspect informs the train crew to take, thereby insuring safe operation of their train. These indications give information as to the allowable speed of interlocked turnouts, block conditions, and information as to the next signal to be encountered.

Early on, the Association of American Railroads (AAR) set guidelines for standard use of signal aspects and indications; however, this did not prevent each railroad from creating its own standards for unique situations. Despite the AAR "standard," railroad signal aspects soon became as unique as each railroad's paint schemes, logo, and structures. This creates quite a challenge for modelers. Not only does one model a particular railroad's motive power and rolling stock, but also its unique operating practices. Modeling operating practices might include modeling a commonly used locomotive consist, the use of two cabooses on a local freight, and of course the railroad's signal aspects.

Many modifications have been made to the C&O's original signal aspects over the years, from the standardization of the three basic signal colors (red, yellow, and green) in 1923 to the use of flashing signal aspects for movement over limited-speed turnouts by CSX. The most notable change for the C&O modeler occurred at 12:01 am on October 26, 1958, when a new Book of Rules took effect. Illustrated in this new Book of Rules were the revised signal aspects and indications showing, for the first time, signal aspects displayed by a three-arm signal. Prior to this, only single- and double-arm signals were used on the C&O. Signals that did not conform to this standard practice (due to unique conditions) would have been listed in the Special Instructions section of the Employee Timetable. Special instructions inform operating personnel of rules and/or conditions that require special modifications from those appearing in the Book of Rules.

To understand why railway signal aspects go beyond using the simplest two-color system of red and green, we must first understand some important train handling factors. A loaded coal train ranging from 90 to 150 cars can weigh 20,000 to 25,000 tons. Depending on grade and track curvature, the distances to stop or safely reduce the speed of such trains can vary greatly. This distance to stop or reduce the speed is referred to as "braking distance" (see C&O drawing M.W. 867 on the facing page for standard braking distances). This also explains why some subdivisions have special tonnage speed restrictions. These speed restrictions (listed in the Employee Timetable) ensure that a high-tonnage train does not exceed a speed that will prevent it stopping within the required distances.

Keeping braking distances in mind, the train crew must have plenty of advance warning of conditions that will affect the movement of their train. These conditions may be anything from an upcoming stop signal to a switch that the dispatcher has set to crossover from one main track to another, or to take a siding. The upcoming turnout may be one of many different sizes depending upon the requirements of the physical track layout, typical use, and the philosophy of the chief engineering officer. Locations where turnouts are employed to cross trains over from one main track to another, or to enter single track from double track, will typically have larger turnouts capable of higher-speed movements than those employed to enter a siding or a branch line. The railroad's objective is to balance cost with efficiency, just as we try to accomplish on our model railroads.

One similarity between model railroading and the prototype is that they both use a numeric system to indicate the size of the turnout. (The NMRA and the AAR, respectively, established these numbering systems.) Although the prototype turnout numbering system is not the same as the model, the basic principle is. The turnout number is derived from the angle of the turnout frog, this measurement being referred to as the "frog angle." The turnout frogs used in modeling are similar to the prototype, and the length of lead and radius of curvature are comparable to scaled-down measurements. In this system the larger the number, the less severe the angle of the frog, therefore simple physics tell us that the larger frog angles will accommodate higher-speed movements thorough them on the diverging route, than those with smaller frog angles. Figure 6 on the facing page shows a chart that I derived for use on my own model railroad. I based this chart on information in the C&O Track and Signal Standards Manual.

With this information one can quickly see why there are so many different signal aspects needed. Not only docs the signal need to inform the train crew of approaching block conditions, and of the next signal to be encountered, but also the speed permitted through a given turnout when it is set to take the diverging route. To make identification of the signal aspects easier and quicker for the train crew the aspects are given names that correspond with the action that must be taken. In conjunction with these names, the speed at which the signal is authorizing the train movement is also named. (See Figure 7 on the facing page for a listing of speed classes with their associated names).

Figure 8 (facing page) shows 12 color excerpts from the C&O's 1958 Book of Rules. Shown are signal aspects and indications illustrating Rules 281 through 292. For the pre-1958 version simply remove any illustrations of a three arm signal (Rules 283-A and 286 are removed in their entirety for this application). We will now look at each signal aspect and indication, and how and where it would most commonly be used.

CLEAR (Rule 281)

This indication undoubtedly is the engineer's favorite as it denotes a minimum of two unoccupied blocks ahead of the train, and all switches within the route governed by the Clear signal are aligned for a non-diverging move.

With these conditions established, the clear indication allows the engineer to operate at maximum authorized speed. This is sometimes referred to by railroad employees as "track speed." Maximum authorized speed varies depending on geography and track structure. It can vary anywhere from 40 MPH in mountainous terrain to 55 MPH on level and tangent track. The maximum authorized speed for any given location on a given subdivision is shown in the Employee Timetable.

APPROACH MEDIUM (Rule 282)

Approach Medium is used several different ways on the C&O. The most common way is to inform the engineer that the next signal to be encountered will restrict train movement to medium speed (30 MPH). That next signal will then require the engineer to have the train at a speed not to exceed "medium speed," encountering there usually a Medium Clear (Rule 283), Medium-Approach Slow (Rule 283-A), or a Medium Approach (Rule 286) indication.

In this arrangement the engineer has the track distance from the Approach Medium indication to the Medium Clear, Medium-Approach Slow, or Medium Approach indication (i.e. one block length) to reduce the speed from maximum authorized speed to the required medium speed.

Another way the railroad uses the Approach Medium indication is to reduce the train speed two blocks in advance of a stop indication (Rule 292). This is used where there is not sufficient braking distance between two signals to safely stop the train. In Figure 9, the maximum authorized speed is 40 MPH with a 0.8% descending grade. This requires a braking distance of 1667 feet. Considering that the distance from signal 72R to 78R is only 1287 feet (380 feet short of the required braking distance) the Approach Medium indication is then employed on intermediate signal 3598. In this application an approaching eastbound train will start reducing its speed upon receiving the Approach Medium indication. The engineer must now have the train reduced to medium speed at or before reaching the next signal (i.e. signal 72R). Using the exact same mathematical formula as before, with the speed reduced from 40 MPH (maximum speed) to 30 MPH (medium speed) the required braking distance is now only 938 feet. This is ample distance for the eastbound train to stop safely at signal 78R.

In a model railroad application I like to employ the Approach Medium indication to simulate short braking distance if the distance between a particular set of signals is less then one average train length. This works quite nicely in the case of a short block where an operator is more likely to miss an Approach indication and run past the next signal displaying "Stop," possibly into the back end of an expensive brass caboose. As we operate our model train across our railroad and encounter multiple "Clear" indications we tend to become complacent and distracted just as the prototype engineers can. This is not surprising, considering that one of the most enjoyable things about this hobby is to socialize with our fellow modelers.

MEDIUM CLEAR (Rule 283)

The Medium Clear indication is used to convey to the engineer that the dispatcher has set a power-operated turnout for the diverging route, and that the speed on that route cannot exceed medium speed (30 MPH). It also indicates a minimum of two unoccupied blocks are ahead of the train. The "diverging route" may be to cross from one main track to another, enter a siding, and/or enter double track from single track.

Figure 10 shows one common use for the Medium Clear indication. In this illustration, the dispatcher has set crossover 9 to the reverse position to cross an eastbound train over from track 1 to track 2 at interlocking (B). Signal 10R is displaying the Medium Clear indication and in addition signal 2R at interlocking (A) is displaying the Approach Medium indication to advise the eastbound engineer of the upcoming medium speed restriction. Once the last car of the eastbound train clears interlocking (B), the engineer may then resume maximum authorized speed.

MEDIUM-APPROACH SLOW (283-A)

The Medium-Approach Slow indication was added to the C&O's Book of Rules in 1958 to provide less-restrictive indications for multiple crossover moves, commonly referred to as over-and-back moves. The Medium-Approach Slow indication is used to indicate to the engineer that the dispatcher has set a power-operated turnout for the diverging route and that the speed on such a route cannot exceed medium speed (30 MPH). It also informs the engineer that he must not exceed "slow speed" (15 MPH) approaching the next signal.

Figure 11 show one common use for the Medium-Approach Slow indication. In this illustration the dispatcher has set crossover 9 to the reverse position to cross a westbound over from track 2 to track 1 at interlocking (B) and back over to track 2 at interlocking (A). Signal 12L is displaying the Medium-Approach Slow indication. The approaching westbound engineer will proceed through interlocking (B) and over to track 1, not exceeding medium speed. He will then proceed, not exceeding slow speed, approaching the next signal (i.e. signal 2L). The next signal "2L" at interlocking (A) is displaying a Medium Clear indication (Rule 283) to cross the westbound back over to track 2. Our westbound train approaching interlocking (A) is already restricted to slow speed by the previous signal indication received at signal 12L (a Medium-Approach Slow indication). This is ample speed to negotiate the medium-speed turnout back over to track 2 as indicated by the Medium Clear indication on signal 2L.

Prior to the introduction of three-arm signal indications on the C&O in 1958, a Restricting indication (Rule 290) would have been displayed on signal 12L in lieu of the Medium-Approach Slow indication for this type of route.

APPROACH SLOW (Rule 284)

The Approach Slow indication is used to inform the engineer that the next signal to be encountered will restrict train movement to slow speed (15 MPH). The next signal will then require the train not to exceed slow speed, usually through a Slow Clear (Rule 287) or Slow Approach (Rule 288) indication. In this arrangement the engineer has the distance from the Approach Slow indication to the Slow Clear or Slow Approach indication (i.e. one block length) to reduce the speed from maximum authorized speed to the required slow speed.

APPROACH (Rule 285)

This indication denotes that the engineer has only one unoccupied block ahead of the train in which to stop, and all switches within the route governed by the Approach signal are aligned for a non-diverging movement. With these conditions established, the engineer must begin reduction to medium speed at or before reaching the Approach indication. In addition to reducing his train to medium speed, he must also take action to be prepared to stop at the next signal encountered.

MEDIUM APPROACH (Rule 286)

The Medium Approach indication was added in to the C&O's Book of Rules in 1958 to provide a less-restrictive indication for crossover moves where the next signal encountered may require the movement to proceed at restricted speed or to stop.

The Medium Approach indication is used to indicate to the engineer that the dispatcher has set a power-operated turnout for the diverging route, and that the speed on such a route cannot exceed medium speed (30 MPH). It also indicates that there is only one unoccupied block ahead.

The "diverging route" may be to cross over from one main track to another, to enter a siding, and/or enter double track from single track. In addition to restricting the movement to medium speed, the engineer must also take action to be prepared to stop at the next signal encountered.

In Figure 13, the dispatcher has set crossover 9 to the reverse position to cross an eastbound over from track 1 to track 2 at interlocking (B). Signal 12L is displaying the Medium Approach indication. The westbound engineer will proceed through interlocking (B) and over to track 1 not exceeding medium speed. He will then proceed, not to exceed medium speed, and prepare to stop at the next signal encountered (i.e. signal 2L).

Prior to the introduction of three-arm signal indications on the C&O in 1958, a Restricting indication (Rule 290) would have been displayed on signal 12L in lieu of the Medium Approach indication for this type of route.

SLOW CLEAR (Rule 287)

The Slow Clear indication is used to indicate to the engineer that the dispatcher has set a power-operated turnout for the diverging route and that the speed on such a route may not exceed slow speed (15 MPH). It also indicates a minimum of two unoccupied blocks ahead.

The "diverging route" may be to cross over from one main track to another, or to enter a siding.

Figure 12 shows one common use for the Slow Clear indication. In this illustration the dispatcher has set crossover 177 to the reverse position to cross an eastbound over from track 1 to track 2. Signal 178R is displaying the Slow Clear indication, and in addition intermediate signal 1654-1 is displaying the Approach Slow indication to advise the eastbound engineer of the upcoming slow-speed restriction. Once the last car of the eastbound train clears the interlocking the engineer may then resume maximum authorized speed.

SLOW APPROACH (Rule 288)

The Slow Approach indication is used to indicate to the engineer that the dispatcher has set a power-operated turnout for the diverging route and that the speed on such a route cannot exceed slow speed (15 MPH). It also indicates that there is only one unoccupied block ahead. The "diverging route" may be to cross over from one main track to another, or to enter a siding. In addition to restricting train movement to slow speed, the engineer must also take action to be prepared to stop at the next signal encountered.

In Figure 14 the dispatcher has set switch 5 to the reverse position for an eastbound to enter the siding at interlocking (A). Signal 6R is displaying the Slow Approach indication. The eastbound engineer will proceed through interlocking (A) and into the siding, not exceeding slow speed. The engineer will then proceed, not exceeding medium speed, and prepare to stop at the next signal encountered (i.e. signal 4RC).

RESTRICTING (Rule 290)

This indication puts much responsibly on the engineer for the safe movement of the train. As stated in C&O's Book of Rules, the engineer must "Proceed prepared to stop short of train, obstruction, switch improperly lined, broken rail or anything that may require the speed to be reduced, but not exceeding fifteen (15) MPH." The statement in this rule "... but not exceeding fifteen (15) MPH" is only applicable in the best of conditions. If visibility is low or obstructed the speed must be reduced below the 15 MPH maximum allowable to permit stopping short of any upcoming obstruction.

The C&O used the Restricting indication in a number of ways: entering a yard, entering a siding, or crossing over from one main track to another if the next signal to be encountered was displaying another Restricting (Rule 290), Stop and Proceed (Rule 291), or Stop (Rule 292) indication.

After the introduction of three-arm signal indications in 1958 the C&O's Signal Engineering office, located in Richmond, Va., began to favor the Slow Approach (Rule 288) or the Medium Approach (Rule 286) indication for crossover moves. This helped in eliminating undue delays to trains by relieving the engineer of preparing to stop short of an obstruction.

STOP AND PROCEED (Rule 291)

The Stop and Proceed indication can only be displayed by an intermediate signal (signals with number plates).

Intermediate signals are defined as "A block signal which conveys Stop and Proceed (Rule 291) as its most restrictive indication." This indication (Stop and Proceed Rule 291) informs the engineer that they must stop at the red intermediate signal and then proceed, being prepared to stop short of an obstruction, or anything else that may require them to stop, but not exceeding fifteen (15) MPH. This allows for greater flexibility and efficiency in the operation of the signal system. For example, if the dispatcher has two eastbound trains to run, one behind the other (less than one block between each other) these two trains can follow one another safely where the second eastbound train will receive a Stop and Proceed indication (versus a Stop and Stay indication). Otherwise they would have to stop and wait until the train clears the block ahead. By allowing this type of following movement, undue delay to the second train is greatly reduced.

Chessie and CSX modelers take note: in the early 1980s the Stop and Proceed Rule 291 was changed to a Restricted Proceed indication. This new indication was intended to save fuel. Studies showed that it took three GP9s 40 or more gallons of fuel to accelerate a 12,000-ton coal train to 40 MPH. With this "new" indication trains were not required to stop, but instead allowed to simply proceed past the red intermediate signal at restricted speed.

See Part 3 of this series (C&O HISTORY, December 2002) for more information on the operation of intermediate signals.

STOP (Rule 292)

Little if any explanation is needed about this indication. One important point that should be explained, in accordance with the C&O's Book of Rules, is that a Stop indication is only displayed by a red-over-red aspect and the absence of a number plate. This explains why home signals that do not govern multiple routes have a fixed red marker light on the low arm.

See Part 2 of this series (C&O HISTORY, January/February 2002) for more information and drawings on this subject.

Looking Ahead

Part 5 of this series will discuss how to accurately model a C&O-inspired CTC control machine, and will provide an overview and comparison of different commercially available model railroad signal control systems that are needed to operate a complete signal system.

Acknowledgments

Special thanks to Jesse J. Smith, Tom Dixon, and John Maugans for their assistance.

Copyright Chesapeake and Ohio Historical Society, Inc. Oct 2003
Provided by ProQuest Information and Learning Company. All rights Reserved