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Single Track Protection Module

Here be the STP, a circuit module that automatically controls signals to regulate two paths of traffic across a section of single track.

Description

A self-contained circuit module with eight train detection inputs, two outputs each for signal and turnout control, three status outputs, and a reset button and input. All inputs expect pulse signals and all outputs are on/off. Each train detection input can be connected wirelessly or by wire independently.

The module manages trains arriving to and departing from the single track on two separate paths (labelled A & B). The paths can cross the single track in opposing directions (e.g. the classic "single track mainline with passing loops" arrangement), converge and diverge in the same direction, be on separate tracks that cross at a level junction, or follow separate tracks through a gauntlet. It can accept any sequence of arrivals on either path. It does not give priority to either path - trains are dispatched on a first-come-first-served basis, and when congested each path will be served alternately - and can handle saturation levels of traffic without blocking the single track.

Each train crosses four detection switches on its path, in the following order:
Approach (a) Start only notifies the module that a train is requesting access to the single track, placed a distance prior to the single track.
Entrance (n) Start only resets the entrance signal to red, placed after the signal protecting the single track.
Clearance (c) End only placed where the rear of the train clears the single track and it is safe for traffic on the other path to proceed.
Exit (x) End only placed where the rear of the train is sufficiently clear of the single track that another train can be sent on the same path without obstructing the single track.

Position the Approach detector such that there will never be more than one train between it and the single track entrance signal (i.e. within the last signal block prior to the single track).

For connecting train detectors by wire use the labelled/colour-coded tabs. To connect wirelessly set passwords in the enlarged labelled/colour-coded remote trigger switches.

The module also offers the option of automatically switching the turnouts into and out of the single track. In the case of an opposing traffic arrangement this action has cosmetic value only, as you can simply leave the turnouts in the correct positions for trains to exit the single track. For converging/diverging uni-directional traffic it will be necessary for the module to control the final turnout to correctly direct traffic, and you can choose whether trains exit on the same path they arrived on, or the opposite path. The orientation of each turnout can be flipped via the onboard on/off switches labelled "Flip Turnout". These switches must be left static once configured or control will break down. Additional circuitry is required to enable changing them during train operations.

The signals controlled by the module must have their source track configured normally. Their range is irrelevant because their aspect is controlled by the remote trigger.

Changing the colour scheme will not affect the circuitry.

I do not require attribution if you incorporate this module into a published layout, but if you do so please post a link in the comments so I can see it in action.

Limitations & resetting

To minimise complexity this module has the following limitations:
- Approach and departure paths are fixed. AI-locking the single track's turnouts is recommended.
- All trains must cross all four of their detection switches in the expected order or control will break down.

Also, unlike the native signalling system it cannot sense when a vehicle has been manually placed on or removed from the track.

Thus you should observe the following for stable operation:
- Do not save the layout while any trains are within or near the detection & control area (the module resets itself when the layout is loaded).
- Do not manually add or remove any vehicles within or near the detection & control area (you can remove them if doing a manual reset).
- Do not reverse over any of the detection switches.
- Resetting restores the module to the "no trains present" condition, so clear the detection & control area before doing so.

Let me know if the module is failing outside these parameters, ideally with guidance for re-creating the problem.

It is theoretically possible for this automation to cause a collision on the single track, but for this to occur two moving trains need to trigger particular pairs of detection switches at the same instant, and only under particular (light) traffic conditions. In theory it is a freak event, one that hasn't occurred in testing. If you experience repeated difficulty with collisions then either you have uncovered a fault that I'm not aware of or the rhythm of your train movements is simultaneously triggering two critical detection switches under specific traffic conditions. Try shortening or lengthening one train (one wagon is enough) to change the switch timings, and if that doesn't work contact me.

How to copy the module to your layout

Use the Bulk move tool (Room.6). Before selecting objects you will need to make the Details (circuitry), Terrain (baseboard) and Room (labels) layers editable. You should see a "Props selected" count of at least 452.

Click Copy and then Done in the tool dialog. Close this layout and open the destination layout. Grab and position another Bulk move tool, open its dialog and click Paste. Then save, close and reload the destination layout (the wiring will not work until this has been done).

Pasting the module into another layout does not create a dependency on this mod. Neither you nor any other user of your layout will need to be subscribed to this mod thereafter.

Application

National Park Automated, the official National Park map augmented with automated signalling and staging yards.

P.S. If you're wanting to trace the circuitry to understand its logic I'd recommend looking at the predecessors to this module, Automated Single Track (Light), Automated Single Track + Turnouts and Automated Single Track (Heavy). This module is built upon a combination of the latter two, but many more components were required to implement the reset function and work around the on/off switch delay bug.