Rail3D*

 

Basic Station Crossover

This article continues on from Basic Through Station.

Putting in a crossover

Suppose now that after we have installed all of our colour light signals, the railway company wants to make our station a terminating location for a small number of trains each day. All the terminating trains will be multiple units, so to terminate and return to where they came from, all they need is a simple crossover so they can get back to the other track.

Let’s create a crossover at the down end of the platform. Insert nodes for each end of the crossover track, one on each track like this:

Now join the nodes together with track to make a crossover:

Open the Edit Node dialog box for the points at each end of the crossover by double clicking on the point nodes. Click the Change Default button until the straight route is selected in red, and type an asterisk ( * ) in the Other Route box. The settings should all now look like this:

These settings tell Rail 3D that the crossover points normally lie straight - for trains on the main line - but that any trains going over them in the facing direction should be routed via the other route (because we don’t want any trains going the wrong way down the main line). The other route is shown in green for you on the diagram of the points in the Edit Node dialog box.

Repeat this process for the points at the other end of the crossover.

One other thing we should do is link the crossover points together. In real life, these points would be linked together so that if one end is set for the straight, then the other end has to be set for the straight too. Conversely, if one end is set for the diverging move to the other track, then the other end has to be set likewise.

To link points together:

  1. Click on one of the points.
  2. Right click on the other set of points.
  3. Select Link Points from the menu (shown below).

To check if the points are linked together properly, go to View > Signal and point links. You should see a purple line connecting the two ends of the crossover together, like this:

Supposing that the terminating trains will be arriving on the down track, they’ll be calling at the station first to drop off the last passengers, and then running past the crossover and reversing back via the crossover to the platform on the up track.

To get the terminating trains to reverse, insert another node a little beyond the crossover on the down track:

On this node, create a Reverse by right clicking the node and selecting Stops and Reverse > New Reverse.

You can now edit the Reverse by double clicking its node.

We set it up like this:

  • The direction arrow must point in the direction the reversing trains will be going before they are reversed.
  • Give it a label - this will probably be the station’s name, but it doesn’t matter too much what you call it for this example.
  • Enter the number of seconds the train will take to reverse. One minute should be enough if the driver is quick about it.
  • Specify which trains should reverse here. Do this by selecting Only routes listed and then type in applicable route names. In this case, all trains on route “LocalDMU” will reverse here. (You can enter multiple routes by separating them with a comma.)
  • You probably won’t want to open any doors here or raise/lower any pantographs!

The last thing to add is a signal for terminating trains crossing back to the up line. You can insert a new node adjacent to the signal on the down line and put one here.

This signal is like all the others, except that I am using the ukr signal type instead. It’s exactly the same as the uk model except that the signal is on the right of the track. In real life you may actually see a shunting signal here but this will be fine for our example. This signal is facing the other way to all other signals on the down line, so make sure it’s facing to the right.

If you place a dmu train on the down track and give it the route name “LocalDMU”, you should see it move up from the station to the reverse, and then change direction and go back to the up track. “Excellent,” you might say. But we’ve forgotten one thing…

Avoiding collisions

Suppose a terminating dmu arrives at the station on the down track. It stops to drop off passengers, then moves up to the reverse. After changing direction it starts to head back over the crossover to the up track. The signal facing it is at proceed, because there are no trains in the section ahead to the up platform. But what happens if a second train happens to be simultaneously approaching on the up line?

One of four things might happen:

  1. The dmu runs into the side of the second train.
  2. The dmu makes it partway to the up line but then the second train smashes into the side of it.
  3. The dmu makes it all the way onto the up line, which causes the signal in front of the second train to suddenly change from “proceed” to “stop” right at the last moment.
  4. After reversing, the dmu starts moving back toward the crossover to switch lines, but then the second train goes past the crossover and is suddenly in the dmu’s signal’s block section, causing the signal facing the dmu to suddenly change from “proceed” to “stop”.

All of these situations are undesirable, to say the least. Two of them are guaranteed crashes, and the other two can easily end up in crashes, not to mention giving the driver a heart attack by changing the signal right in front of him/her.

To prevent all of this happening, we make all signals governing moves over the crossover controlled signals. This means opening the Edit Node dialog box and setting the Controlled option for each of them.

By setting a signal to controlled, it will show “stop” by default. The only time it shows anything else is if a train is approaching and wants to pass it. To do this, the signal determines where the train wants to go and checks to make sure that the track is not occupied by another train. If everything is clear, the signal sets a route over the track and then shows a “proceed” aspect.

When deciding if the track ahead is clear, the signal must also make sure that no other signal has set a route over the same track. If a conflicting route already has been set from a different signal, then the train will just have to wait until the track becomes free.

Remember: if there are any points or junctions whatsoever after a signal and before the next signal, then the signal needs to be controlled. (There are also other reasons signals might be controlled, but that’ll do for now.)

You can turn on signal locking and routing (go to View > Signal locking and routing) to see where routes have been set. In the screenshot below, the dmu has been cleared to cross to the up line, while a goods train has to wait on the up line.

The reserved route set from the signal is indicated by a green line and occupied sections of track are shown in red. You can see that the goods train can’t possibly be given a “proceed” aspect by its signal because the signal would need to reserve a route that is in conflict with the dmu’s route.

In Rail 3D, the reserved route actually corresponds to track links. Each link comprising the reserved route is individually reserved. Once a train moves onto a track link that it reserved (green), the link becomes occupied (red) until the train moves off the link, whereupon the link is then freed so that other signals can reserve it.

If at any time you need to cancel a route set from a signal, you can right click on the links that have been reserved and select Clear Section from the menu. However, exercise caution if you do this, because you could easily send two trains heading straight for each other!

25 January 2007

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