Model Railroad Signal System Planning

Many model railroaders have approached us and asked: "What is the first thing I need to do to implement a signal system?  I want signals and don't know where to start.".  This is a valid but loaded question!  There are numerous other questions to be answered as part of this question.

This question is similar to asking about implementing an operation governed by a Timetable & Train Order system.  With T&TO operations, you don't have the physical wayside equipment like with a signal system, but there are still elements to consider that make up this system of operation.  You might need to think about how you would operate like this.  Questions like: Where are my stations, passing sidings and other mainline points of importance such as junctions need to be identified.  The type of trains and the number of them you expect to run on your layout would also be important to consider setting up your operation.  Then, once you have an idea of what you want your layout to do, you actually need to implement the T&TO system.  What exactly is this, and how did real railroads actually implement this?  How did this system of train control actually tie into day-to-day railway operations?  How can I mimic this in my hobby?

Without understanding what the underlying system is supposed to do, we can not actually model a system that reflects reality.  We could conjure up an idea in our heads about how the railroads would have done this, but without actually examining how a real T&TO system worked, we would never generate a system that reflects how the railroads actually did it.  At best, it would be a poor approximation, but it would work as we imagine it should.  Fellow operators that are familiar with this type of operation would immediately notice the departure from reality even though to you, this is how your railroad works and it fits your view of railroading.  Artistic license is fine, but to a point.  Too much departure from reality tends to diminish the results of our labors.

The very same can be said of modelling railroad signal systems.  You may notice wayside signals along the railroad you model or upon a fellow model railroader's layout, but without understanding how they tie into operations and what they do, you will not generate very good results.  In addition to the actual operational relationships, you also need to understand some of the general guidelines used in placing signals and related equipment.  One of the most common mistakes made by model railroaders is the actual placement of signal masts relative to trackwork and where train detection (track circuits) is required. So where do we start?  I always suggest the following checklist of items to consider:

1. What railroad are you modelling?  Did this railroad use signals?  If so, what type of signal system did they use?  This isn't a question of manufacturer, but rather of the type of operating rules that were used.  Absolute/Permissive Signals (APB) and Automatic Block Signals (ABS) are signal systems that help trains keep separated from each other and safe from conditions such as mis-lined switches or broken rails.  However, the signals themselves do not convey authority for the train to use the mainline.  Either timetable rules or other written authority rules are typically used with these types of signals.  Centralized Traffic Control (CTC) is a type of signal system that does convey authority to use the mainline and utilizes a dispatcher in a central office to govern the movement of trains by setting the remote signal system to provide authority to trains as they move across the railway.  Terminals such as large stations may have an isolated signal system to govern large numbers of trains through complex track work.  This is typically the most complex version of interlockings found on the railway, but CTC is made up of many less complex interlockings that are controlled remotely.
   
   
2. What parts of your layout is mainline?  Signaling typically exists on mainline only.  Storage tracks, industrial spurs and yards are generally not involved.  Whether you have an existing layout or planning a new one, identify which tracks would be considered the mainlines and passing sidings.  Any sidings that are for storage only, don't consider them.  Draw a straight line drawing of your layout, only including the mainline components.  This drawing is where you will plan your signal system.  Depending on the type of signal system you want to implement, you can now start to plan where you need signals and which turnout switches need to be interfaced with.  Any turnout that connects to mainline should be considered, even if it connects to non-mainline trackage.
   
   
3. What elements of a signal system need to be considered?  Signal systems in their simplest consideration are made up of physical inputs and outputs.  Inputs to a signal system are usually: train detection (blocks and track circuits) and switch positions.  Outputs are generally signal aspects and turnout switch control (CTC and interlockings in particular).  A list of these inputs and outputs can be tabulated to derive how much equipment you need to operate the entire layout.
   
   
4. What type of hardware do I need to operate my layout?  There are numerous suppliers of signaling equipment.  These typically range from simple to install but lacking in realism, to more flexible in implementation but more difficult to configure.  Then there is the question of whether a centralized control system can be implemented with cables running to points along the layout, or if a distributed system is more suitable.  The latter is typically the only viable option for modular and sectional layout designs.  The Signalogic Systems DBM signal controller is able to provide either configuration style with sophisticated control and easy setup using our Signal Configuration Suite freeware software.  Typically, centralized installations with the DBM controller are very economical.
   
   

Another thing we hear from model railroaders is that the notion of building such a system is overwhelming to them.  I believe this is also a product of a lack of knowledge and experience in the matter.  A skilled modeler would know that you could not scenic an entire layout in one short duration.  In fact, you'd probably start with basic scenery and over time develop the complexities.  The same can be said with a signal system as well.  Don't try to eat the whole cow at once.

My advise to people planning a signal system is to start slow.  Understand the four points above and have a plan.  When it comes to implementation this can be done in steps.  Turnout switch control is a fundamental input to the system.  So is train detection, but in actuality, train detection can be one of the last things to implement as you develop your system.  By having turnouts wired up for signaling in advance, you can start to implement your signal system to react according to switch position only and then build up detection as time goes on.  Customers have found this method rewarding as they see their system slowly get more functional as they add more and more equipment.  This helps drive initiative to continue on which is often welcome!

Signalogic Systems provides a comprehensive array of products to provide all inputs and outputs to your signal system.  Our line of switch control products uses a standard two-wire I/O independent of the switch machine type.  This two wire interface can be connected to standardized fascia mounted switch control panels or to our standardized DBM signal controller.  Our line of train detection products continues to grow as well.  Feel free to continue using a varying array of switch motors.  We will work to develop new interfaces as new options emerge.

The DBM signal controller is where all the magic really happens.  The DBM understands signaling on its own, and can independently operate a signal system without need for a computer.  It can operate up to 32 signals and 32 switches.  Different types of I/O modules can be used based on your specific needs, including output drivers for common-anode, common-cathode and bicolor LEDs.  These can be mixed on one DBM for when different types of signals are used on a layout.  Signals can be defined to use up to 16 LEDs, a full 3-head signal only uses 9. With Signal Configuration Suite, you can create your layout by simply drawing your mainline like you did on paper in point #2.  The most complex part of the configuration process is deciding where to connect your inputs and outputs to the DBM controller.  Signal Configuration Suite will configure the DBM for your layout specific requirements based on information you provide such as type of signal system and railroad specific behaviors.

Implementing a signal system doesn't need to be reserved only for the most computer savvy modelers.  Signalogic Systems understands that operations minded hobbyists want to operate their layouts realistically, not program their layouts hour months on end to achieve their desires. Contact us if you have any questions about how we can help.