Hidden Sidings And Depots

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The aim of this section is to have a look at some of the signalling issues involved in getting trains into and out of a set of siding tracks in Rail3D. We’ve already seen one approach to this in the Two-track Terminus, where we use the Free Route option to divide trains between the two platforms.

Hidden Sidings

The specific example I’m going to look at is a feature found on many model railway layouts — the hidden sidings (sometimes called a fiddle yard, or Schattenbahnhof). Modellers use these because they only have space on a layout for a very short stretch of track the equivalent of 1km in real life is 11.5m in H0 scale or 6.25m in N; in Rail3D we have essentially as much space as we need, but we are usually only interested in part of a particular railway system. So we may well need some kind of storage area that trains can disappear into when they leave our part of the system, to reappear later on and — preferably — in a different sequence.

Track Layout

The basic track layout is as simple as possible. Trains come in on the main line, are turned round by a balloon loop, and distributed into a classic “fan” of sidings. At the other end, the sidings feed back onto the main line. I’ve added a trailing crossover to make sure that any train that accidentally gets reversed is sent back to the main layout on the correct track.

Arrivals side signalling

As with the Two-track Terminus, we need to protect the crossover points with a Controlled Signal. It makes sense to add a Speed Limit for arriving trains as well.

I usually put at least one Automatic Signal in the balloon loop so that, if anything goes wrong, arriving trains can queue in the loop rather than on the main line. If you have a tunnel that is supposed to represent “the main line to Scotland” it looks a bit silly if there are trains queueing to get into it…

The last signal in the balloon loop controls the distribution of trains into the various sidings. This should therefore also be a controlled signal.

The points leading into the sidings have to be set up with “*” in the Free Route box. This tells the controlled signal to choose whichever path through the switch is free. If more than one path is free, it should decide randomly.

There is one small complication in this — for free route through a series of switches to work correctly, it is important that the switches are arranged with the “main” (default) path leading to the next switch and the “other” (non-default) path leading into the siding. This means that, in contradiction to the usual practice, if you have laid the track as in the illustration above, the first switch in the chain (the one on the right above) should be set with the curved path as default. To change the default path, double-click on the node to open the Switch Options dialogue, and press “change default” until the red (default) path in the little diagram is pointing along the curved route and the green along the straight.

Departure side signalling

This is where it gets interesting! We could just set up each track with a Stop feature and a controlled signal, so that arriving trains would be held for a predetermined length of time, or until a timetabled departure time.

A more interesting approach is to use a feature we haven’t met up to this point: Hold Signals and Releases.

A Hold Signal works like a normal controlled signal, except that it cannot clear until a linked Release feature has been triggered by the passage of a train. The most common use of this is to place the release a short distance before the signal it is linked to, to delay the clearing of the signal and hence ensure that the train has slowed to a safe speed for a junction or terminus (cf. Speed Proving). However, you can also use a release triggered by a train on a different line.

This is what we are going to do here — we want a train arriving in one siding to release a train held in a different siding. This way, trains will depart from the fiddle yard at roughly the same frequency as they arrive, but not necessarily in the same order. For example, if the yard has five tracks, we could set it up so that:

• trains arriving in track 1 trigger the release for the exit signal of track 2
• trains arriving in track 2 trigger the release for the exit signal of track 3
• trains arriving in track 3 trigger the release for the exit signal of track 4
• trains arriving in track 4 trigger the release for the exit signal of track 5
• trains arriving in track 5 trigger the release for the exit signal of track 1

Creating Holds and Releases

The first step is to place an exit signal for each track. It is a good idea to make sure that there is at least one node between the signal and the converging switch (otherwise it could happen that a train overrunning the signal slightly blocks the adjacent tracks).

Set the direction of the signal and choose a suitable signal model in the signal dialogue, as usual (I used an overhead signal type because the tracks are close together — you could also use a ground signal). Select the Controlled and Hold options.

With the signal node still selected, right-click on a node near the arrival end of one of the other tracks and select Signals|Link to New Release from the context menu.

You will see that a Release feature has been created. Double-click on the node to open its properties and check that it is pointing the right way. For this project we can leave the route options set to All Trains.

To check that we have set it up correctly, you can turn on Show Signal and Point Links from the View menu. You should see a line linking the release to your signal.

Now we just have to repeat this for all the other tracks, making sure that each release is linked to a signal on a different track.

Trying it out

For testing, you will need to extend the main line a little way, and put some kind of reversing arrangement at the far end of it. You could use the Two-track Terminus layout, or a simple 180 degree loop, according to taste. Put a few automatic signals on the main line, so that it can hold several trains.

Send a few trains down the line into your yard. You should see them sort thenselves randomly into different tracks. The trains will be held until another train comes along in the appropriate track to trip the release, so you should get a (slightly) random traffic order down the main line.

Taking this further

Although I’ve described a “fiddle yard”, you could apply the same basic idea to any situation in which trains have to be stored in a set of sidings. Examples could include holding sidings for goods trains, a depot where trains are stabled overnight, even platforms at a large station. The same arrangement can easily be modified to use dead-end sidings with Reverser.

David Morley has described a method for automating a Motive Power Depot using Scripting. In principle, you could also use scripting to create a sort of train source/sink, that takes an incoming train and replaces the vehicles with a different type. However, this is still relatively untested.

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