Advanced signalling examples

From OpenTTD

For general information about signals, and instructions on how to build them, see the main signals article

To Do
Tidy this up into a proper showcase of complicated signaling arrangements. Maybe even export it all to new types of Junctions or into Stations.

Fig 3. - Pre-signals used to their full potential.

To Do
Label the above image and explain what's going on

[edit] Pre-signals and a single track intersection

This example should give you a good idea of the help that pre-signals can be, and an example of combo signals.

Say you have two trains, each going to their own stations, which both travel along a single north-south track for part of the way. You'd use regular two-way signals where the lines switch onto the single section (four in total, one for each switch).

What if you want a new east-west track to cross the north-south track? Let's say you don't want to use a bridge, and your new east-west track is a high-speed service. It can't wait for northbound and southbound trains to clear the whole single section. You run the tracks across each other, and make a 4-way intersection surrounded by regular two-way signals. The problem: the signals break up the north-south section of track, meaning a northbound train could meet a southbound train at a red light at the intersection.

The solution: Pre-signals. Set up entrance pre-signals (horizontal yellow) where the trains on the north-south line switch onto the single track. At the intersection, set up combo pre-signals (vertical yellow) on the north-south line. (You can keep using normal two-way signals for the east-west line.)

How it works: Call the southern entrance signals AB, the combo signals at the intersection X (south side) and Y (north side), and the northern entrance signals CD. A northbound train enters the single track at AB. AB works just as normal signals. X turns red for southbound trains. X is an exit signal for Y, so Y also turns red for southbound trains. Y is an exit signal for CD, so they both turn red for southbound trains too. In the meantime, an east-west train can pass through. Here it is the other way around: A southbound train enters the single track at CD. Y turns red for northbound trains, and Y is an exit signal for X, so X turns red, which is an exit signal for AB which also turns red.

To Do
Some images should help

[edit] Optimal pre-signaled station

Below is an image of an "optimal" Pre-signal station layout. With these signals trains will choose any free platform and if none is free it will wait at the entrance instead of brutally picking one and waiting for that train to leave.

Fig. 4 - An "optimal" RoRo station layout with presignals.

Explanation of the signal types:

• Signals 1 through 12 are Pre-signal Exits
• Signals A, B, C and D are Combo Signals
• The signal E is the only Pre-signal (Entrance)

How they operate:

• If signals 1, 2, 3 and 4 are red then signal A will be red.
• If signals 5, 6, 7 and 8 are red then signal B will be red.
• If signals 9, 10, 11 and 12 are red then signal D will be red.
• If any train is between signal A and signals 1, 2, 3 and 4 signal A will be red.
• If any train is between signal B and signals 5, 6, 7 and 8 then signal B will be red.
• If any train is between signal C and signals A and B then signal C will be red.
• If any train is between signal D and signals 9, 10, 11 and 12 then signal D will be red.
• If any train is between signal E and signals D and C then signal E will be red.
• If signals A and B are red then signal C will be red.
• If signals C and D are red then signal E will be red preventing access to the station.

Below is an animation of how this would work in the game.

Fig. 5 - How the "optimal" RoRo station would work with presignals.

As the animation shows trains can choose any track without too many problems.

[edit] Another example

Fig. 6 - Station with presignals.

[edit] Free tracks

Using presignals to allow trains to use spare tracks more intelligently

Suppose you have two tracks leading from two sources to the same location. You want each source's own traffic to have priority on its own track but want to utilize spare capacity on one of the tracks because the other is getting busy. This can be achieved with presignals.

In the diagram, the two tracks are labelled A and B leading into tunnels A and B respectively. Track A is the one with a less frequent service whose spare capacity we want to use. Track B is very busy and needs some breathing space, which we can get by diverting traffic onto A. However, what we don't want to do is let B's traffic disrupt the service on A - in other words A needs priority on its own tunnel. We arrange this by using presignals.

Assume each of the tunnels is signaled at the opposite end so that when a train leaves the tunnel the signals at this end clear. So signal 1 will show green when tunnel B is clear, which will in turn make entry presignal 4 green. The interesting part comes when tunnel B is blocked, so 1 is red. In that case we want an incoming train to use tunnel A, but only if there isn't a train on track A wanting to use it.

We connect the tracks as shown and place signal 3 as an exit signal to 4 so that a train coming up to 4 can use either 3 or 1, whichever is available. Now, we need to stop 3 showing green if a train on A needs to use the tunnel. To do this we simply make signal 2 a bi-directional exit signal. Then if there is a train in the block before it on A (i.e. one with priority on the tunnel), the back of the signal will show red, otherwise it will of course be green. Then, if we make 3 a combo signal, it will show red in two cases:

1. A train is in tunnel A
2. There is a train on track A coming up to use the tunnel that should be given priority (because signal 2 will be red and it appears as an exit to 3 even though that isn't possible with the track layout)

So when 3 is red, a train on B is only allowed to proceed on its own track.

In that way, trains on B use track A if there is spare capacity but any vehicles already on A get priority.