What model railroad signals do
On a real railroad, signals tell crews whether the track ahead is clear and which route a train will take. On a model railroad, working signals can do the same job: they change their aspects (the colors or positions displayed) depending on what is happening on the layout. For many modelers they are mainly a realism feature, and for layouts that run trains with dispatching they can also help crews know what is going on. If you are interested in the bigger picture, see our overview of model railroad operations.
Signals are not traffic lights
Railroad signals are not traffic lights. Their colors do not always mean what drivers expect, and the meanings differ between railroads and eras. A red signal may mean stop, but a yellow or green aspect can carry different instructions depending on the signaling rules in use. Some masts carry two heads, and that arrangement often relates to a diverging route at a turnout.
Because of this, it helps to research the signal practice of the railroad and period you model before choosing hardware. If your layout is freelanced, pick a prototype whose signaling you like and follow its general approach.
Three levels of signaling
Signaling ranges from simple to complex. It helps to decide which level fits your skills and budget before buying anything.
- Decorative signals. Signals are installed with lights that stay on or are switched manually. This is the easiest way to add the look of signals.
- Standalone automatic signals. Self-contained systems change aspects based on a simple input, such as a train being detected in a block or a turnout being thrown. They need no computer.
- Computer-controlled signaling. Software reads block occupancy, turnout positions and other sensors, applies logic, and tells signal hardware what to show. This is the most flexible and realistic option, but also the most involved and usually the most expensive.
If your DCC system cannot connect to a computer, check that before planning a computer-based setup.
Start with a signal plan
A signal plan is a marked-up copy of your track plan. Making one before you buy parts lets you see how many signals, detectors and wires you will need.
- Draw your track plan.
- Mark where signals will go, following the practice of the railroad you are modeling.
- Decide what should change each signal: a block being occupied, an on-switch (OS) section, a turnout position, or a combination.
- Mark where track must be gapped and number blocks, turnouts and signals.
- Count the totals to estimate equipment.
You can choose to signal only part of the layout, such as a main line or a single junction. Starting with one area is a sensible way to learn.
Block detection
To know where trains are, the layout needs detection. Two common approaches are:
- Current detection. A sensor notices current drawn by locomotives or by cars with resistor wheelsets or lighting. The track section is normally isolated by gapping one or both rails, depending on the manufacturer’s instructions.
- Optical or infrared detection. Sensors notice the train passing without relying on current.
Block length is up to you. A common rule of thumb is that blocks should be at least as long as your typical train, and sidings should fit a full train, but there is no single right answer. Follow the instructions of the detector you choose, because requirements differ between products and between DC and DCC.
Turnout position detection
The signal for a route often depends on how a turnout is lined. Position can be detected in several ways. Some turnout machines have auxiliary contacts that report position. In some computer systems, the same command that throws the turnout is also used to indicate its position, though that does not confirm the points actually moved. Choose whichever method your turnout hardware supports.
Signal types and aspects
Signals come in several styles, including color-light signals, searchlight signals, semaphores and low dwarf signals. Heads may have one, two or three lamps, and some models mix more. Your choice depends on your prototype and scale. Semaphores add moving blades, which usually need a small motor or turnout machine to drive them.
Wiring the signals
Most modern model signals use LEDs. A few points to keep in mind:
- LEDs generally need a current-limiting resistor. Follow the signal maker’s instructions for the value and where it goes.
- Check whether your signal uses a common anode or common cathode wiring, because this affects how it connects to a controller.
- Signal wiring can multiply quickly, with several wires per head. Labeling wires and using plug connectors make troubleshooting easier.
- Signal decoders and boards take commands and drive several heads, which reduces the amount of wiring you must do by hand.
Always follow the manufacturer’s wiring diagrams for your specific parts. Wiring can differ between product lines; for the general principles of buses and feeders, see our guide to model railroad wiring diagrams.
Software and logic
Computer-controlled systems read inputs and produce outputs using rules. Free software such as JMRI is widely used for this, and it offers signal logic tools that can calculate aspects from block and turnout status. Other layouts use dedicated hardware logic instead. Whichever you choose, the program needs to know about your blocks, turnouts and signals, which is another reason to number everything on your signal plan.
Choosing equipment
Several companies make detectors, signal boards and signal heads, and some systems are designed to work together. Staying with one product family can simplify the work, because the parts are meant to connect. Check compatibility with your command system and your turnout controls before you buy. Starter sets from some manufacturers include a signal, a control board and a cable, which can be a way to try signals before committing to a full system.
Cost and effort
Working signals add cost and effort. A detailed system can need many detectors, many signal heads and a lot of wiring. Planning ahead and building in stages helps. Since signals need reliable track and detection to behave well, make sure the basics are working first.
Mistakes to avoid
- Buying hardware before making a signal plan.
- Ignoring prototype signal rules and ending up with confusing aspects.
- Skipping resistors or ignoring wiring instructions for LEDs.
- Choosing detectors that are incompatible with your command system.
- Trying to signal the whole layout at once rather than one area.
FAQ
Do I need a computer to have working signals? No. Simple standalone systems operate without a computer, though computer control is more flexible.
Do grade crossing signals work the same way? Crossing signals and bells use different controllers and are generally a separate topic from block signaling.
Where do signals fit with operating sessions? If you use a dispatcher or timetable, signals can show crews track status. A fast clock is another tool that often pairs with them.