Prototypical Mainline & Yard Signaling
By Don Woodwell

(excerpted from Automating Your Model Train Layout, 2nd Edition)

In the days of early railroading, when a train was sent along a track occupied by another train, there was a real possibility that the second train could catch and collide with the rear end of the first loco and its' cars. The trick back then was to time-space the two trains to avoid conflicts. If the two trains did not occupy the same stretch of track at the same time, they obviously couldn't run into each other.

Such simple logic still exists to this day on some roads where traffic is light. Time-spacing was accomplished by signaling systems that were first created by individual railroads but ultimately became standardized as trains shuttled from one line to another.

Early signaling systems like those of today accomplish three basic tasks: allow trains to follow one another without rear-end collisions; get them through junctions, crossings, and yards without mishap; and safely and quickly handle opposing movements on single track.

An alternative principle for keeping trains apart is the “space-interval” or “block” system. Manual block systems maintain the necessary space between trains whether or not they are behind schedule, and are more concerned with safety than capacity of track. On our high-rail and scale layouts, collision avoidance is our primary concern so that manual or semi-automatic blocks are just as effective as on the 1:1 scale roads.

Commercial electronic modules activate and coordinate signals with train movement on a model train layout. Detectors, timers, and relays are particularly important and these and other means of controlling signal aspects are described.

Signal Types

In order to illustrate the installation and use of signals, I have chosen the searchlight type for my own layout, NC-Lines, a fictional North Carolina short line railroad. The searchlight signals have a two-color LED, red or green. One head is sufficient to show Stop and Clear aspects, and a second head is needed for a Medium Clear aspect. Approach Slow with yellow LEDs and Slow Clear are other aspects used by NC-Lines.

Figure 1 - General Signal Types & Aspects, Rules, Descriptions

The signal system rules shown in Figure 1 are similar to CSX Transportation, Norfolk Southern, BNSF, and UP rules not just for signaling but also for all aspects of conducting transportation over their rail networks.

Obviously, a large number of signal aspects make for a more prototypical layout, but installation complexity increases rapidly. If you enjoy the challenge, then by all means, add as many signals as you need. But start off with basic signals and then grow as your time, money, and patience allow.

Signal Planning

Illustrate your layout as a series of straight-line sketches. Figure 2a show NC-Lines' east and westbound mainline. Figure 2b shows bi-directional passing sidings #3 and #4 as well as stub sidings.

Figure 2a: NC-Lines Mainline Signal Planning	Figure 2b: NC-Lines Mainline Signal Planning

NC-Lines' mainline and yard approaches utilize searchlight signals, and each signal is equipped with either single or bi-color LEDs. Bi-color LEDs are two color combinations of red, green, or yellow. Based on the aspects to be displayed, it is necessary to specify the number of heads per mast in one or two directions.

Figure 3a - NC-Lines - Signals A1/A2 East & Westbound Mainline	Figure 3b - NC-Lines - Signals B1 & B2, Diverging Routes
Figure 3c - NC-Lines – Signals C1/C2, E/W,Yard Entrances

Since NC-Lines' mainline is bi-directional, most signal heads are mounted back-to-back on a single mast. Double track mainlines with two-way movement require two signals for each direction of travel, and are often mounted on overhead signal bridges.

Figure 4: Yard Entrance Signal C2, Westbound

Turnout position controls NC-Lines' mainline signals aspects. The reason for this approach is simple: The direction and location of the train determines which aspects are shown to the engineer. No other detectors are needed on the NC-Lines' mainline and the yard leads.

For example, if turnout T2 is set for the diverging route on NC-Lines, the signal A2 is set for Medium Clear, that is proceed at a medium speed [30 mph on most roads] for eastbound trains, see Figure 5a), and B2 is set for Medium Clear for westbound trains (Figure 5b).

Figure 5a: Medium Clear Aspect, Signal A2 Headed Eastbound at Turnout 2	Figure 5b: Medium Clear Aspect, Signal B2 Headed Westbound at Turnout 2

Signal Plans & Installations

Planning - The key to successfully running with signals is planning each signal and block action a step at a time. Thinking ahead in the early stages may save many aggravating hours of rewiring signals, detectors, and blocks later on as your signaling becomes more complex. Practical multi-train operations with automatic control are ensured with the right mix of signals and blocks.

First, create a total plan and then install signals and controls in stages. Initially, you may choose to place signals on only part of your layout, for example mainline or yards, in order to reduce complexity and cost. As your layout and operations expand, you may also proportionally increase the number of signals and electronic controls in order to ensure realism.

Command control operations are enhanced by the appearance of prototypical signaling even though blocking is not automatic but controlled by the command control operator. Nevertheless, planning and setting up a realistic signaling system with proper aspects follows the same steps as described above.

Installing - Mounting the scale Shiloh signals requires drilling a 1/8” (32mm) hole and pushing the mast into the hole. Use a small amount of white glue to hold the mast in a vertical position. The simulated concrete mount attached to the lower mast ensures that the mast is mounted a scale 20 feet above the ground surface.

Signaling Wrap Up

Because he cannot steer his train, the engineer must rely on the order board, semaphore, or colored light to provide the space between his train and the next one on the same track. He also needs the signals for safety in yards and when entering the mainline. You, too, can help your engineers with signaling of many kinds to provide safety and collision-free running on your high-rail or scale layout. Give it a try and the mysteries of modern model signaling will soon disappear.

Prototypical Signaling References:

• Armstrong, John, “All About Signals” [part 1], Trains, June, 1957, Kalmbach Publishing Company, 21027 Crossroads Circle, P.O. Box 1612 , Waukesha , WI 53187-1612

• Armstrong, John, “All About Signals” [part 2], Trains, July, 1957, Kalmbach Publishing Company, 21027 Crossroads Circle, P.O. Box 1612, Waukesha, WI 53187-1612

• Melvin, Rich, “Prototype Signals, Part 1”, OGR the Video, Vol. 3, No.3, Myron J. Biggar Group, Inc., Spring, 1996

• Melvin, Rich, “Prototype Signals, Part 2”, OGR the Video, Vol. 3, No.4, Myron J. Biggar Group, Inc., Summer, 1996

• Rich Weyand, TracTronics, Inc, Articles on 'Electronics for Operations', 1994, Mainline Modeler magazine, ph. 630-527-0000, rich@tractronics.com

• Additional Background at the signaling Web site: http://www.lundsten.dk/us_signaling/index.html

• Signal Rules Demonstrator

http://raildata.railfan.net/java/DivRte/NORAC.htm