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Automated Single Track (Heavy Traffic version)

A bare layout with a single track section controlled by automation tools. To see operation, remove the two loose tank wagons that are blocking the AI trains.

Single track protection circuitry is now available as a self-contained module.

This configuration is suitable for heavy traffic. If saturation occurs in either or both directions the single track will always clear. For settings where saturation is not of concern, the simpler Light Traffic version of this automation can be found here.

How to perform a manual reset

If control breaks down you can manually reset the system by:
1. Clearing all trains from the detection & control area (which includes the single track section).
2. Setting all 11 lever switches to the off position. Move from right to left to avoid them switching back on automatically.

Description

This setup was created because the game's native signalling system is currently unable to safely manage a section of single track, as I discovered when trying to run additional traffic on the National Park map.

The fundamental principle used is that of "track possession", which is only given to one train at a time.

The entrance signals to the single track section are controlled by the automation. All other signals are configured normally. Exit signals from the single track section are not necessary but you could place some if you wanted to.

To minimise complexity this system is not very intelligent and has the following limitations:
- Paths are fixed. In this example all trains must keep left. The turnouts are AI-locked.
- All trains must cross all four of their detection switches in the expected order or control will break down.
- 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:
- Do not save the layout while any trains are within or near the system's detection & control area.
- 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.

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

It is theoretically possible for this automation to cause a head-on 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 traffic conditions. I haven't had this occur in testing. I have yet to find a simple way to eliminate this small risk. If you have repeated difficulty with head-on collisions then it means that 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.

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