Signals

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'''Semaphores''' are a type of signal with no functional difference from regular signals.  They simply have a different (old-style) appearance.
 
'''Semaphores''' are a type of signal with no functional difference from regular signals.  They simply have a different (old-style) appearance.
  
Before OpenTTD 0.6.0 semaphores were only created by holding ''Ctrl'' while placing the signals. Since 0.6.0 semaphores will be created instead of light signals before a configurable year, 1975 by default. This setting is called "Automatically build semaphores before" and is in the "Construction" tab of "Configure Patches".
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Before OpenTTD 0.6.0 semaphores were only created by holding ''Ctrl'' while placing the signals. Since 0.6.0 semaphores will be created instead of light signals before a configurable year, 1975 by default. This setting is called "Automatically build semaphores before" and can be found in the "Advanced settings" under "Construction" and then "Signals".
  
After placement, holding ''Ctrl'' and clicking changes the extended signal status of the signals (i.e. presignals). You cannot change pre-placed semaphores to signal lights,though you may remove them and re-add them as you wish.  In version 0.6.0 and above, you can also use the signals GUI to place this type of signal.
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After placement, holding ''Ctrl'' and clicking changes the extended signal status of the signals (i.e. presignals). You can change pre-placed semaphores to light signals by choosing the "convert signal" tool from the signal-gui and ctrl+clicking on an existing signal.
 
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===History===
 
===History===

Revision as of 11:50, 2 March 2009

See the Building signals tutorial for a practical introduction to signalling

Signals are useful devices that allow you to control train movement. They are necessary to keep trains from crashing on railway networks with more than one train.

Contents

Signal Construction

Signal build mode

To do any construction work with signals, you need to be in signal build mode. Open the Railway Construction toolbar and click the signals icon to enter this.

Then, while in signal build mode:

  • To place a signal, click on a clear section of track. To begin with this will be a two way signal, the most basic type. See below for how to change this to a different type. If placing a signal where two parallel tracks share a map square, ensure you click on the precise track you wish to signal.
  • Place multiple signals at the same time by clicking an existing signal and dragging the mouse cursor along the track. They will be spaced as set in the Drag signal density patch and will face the same way as the signal you started the drag on.
  • Place multiple signals along an entire line of track by holding down Ctrl and dragging from a signal already placed. You need only to drag one square and it will auto complete the entire line of track, based on the Drag signal density until either a station is hit or a fork in the track. (0.6.0-beta 2)
  • Remove signals by clicking the Toggle clear active.png bulldozer button (while remaining in signal build mode) and then clicking on the unwanted signal. You can drag to remove multiple signals.

You cannot construct signals on a square shared by more than one piece of track unless the tracks are parallel.

New Signal GUI in 0.6.0

Since 0.6.0, a new signal interface can be used to place signals. In openttd.cfg set enable_signal_gui as true and when you click on "build signals" you will now get this interface:

(on the right)
File:Signalgui.PNG
New Interface.
Column 1 Column 2 Column 3 Column 4 Column 5
Semaphore
(Standard)
Semaphore
(Pre-Signal)
Semaphore
(Exit-Signal)
Semaphore
(Combo-Signal)
Convert to selected
Electric
(Standard)
Electric
(Pre-Signal)
Electric
(Exit-Signal)
Electric
(Combo-Signal)
Auto Build Density

This is to prevent the tedious ctrl-click cycling through of the signals (even though I do prefer it) The "Convert to selected" converts the signal type on the track to the one selected in the gui. The Auto Build Density show you how close the signals are placed when auto build of signals are used.

Two-way signals

Two-way signal.png
Two-way signals at a loading station

Two-way signals are used in a railway that has trains moving in both directions on the same track. The most common use is at end-of-line stations, where trains enter and exit the same end of the station. In the example at the right, the signals direct the next train to come to go to the empty loading bay. They also prevent the train from leaving the loading bay if another train is in the way.

If a train has a choice of two or more directions, each with two-way signals on them, it will choose the direction with a green signal. If all signals are red it will pick the easiest direction and wait for the signal to change.


One way signals

One-way signal.png

One-way signals limit train movement to one direction. In the example below, the signals force the trains to move in a circle. This has two advantages: trains enter and exit stations efficiently, and the track can have more than 2 trains.

When using one-way signals, be sure that they are all facing the correct direction. It is a good idea to watch the first train you run on the newly signalled line all the way to its destination to ensure you haven't made any mistakes.

Click on an existing two-way signal to toggle it to a one-way signal. Click on it again to change its direction (leaving it one-way); the third time will revert it back to a two-way signal.

If a train has a choice of tracks, each with a one way signal, it will pick the track heading towards its destination (i.e. it will wait until the signal on the track heading towards its destination turns green, as opposed to taking whichever signal is green if one of the signals is red). This is in contrast with two way signals.

If a train arrives at the wrong side of a one-way signal it will immediately reverse.

One-way signals in a loop

Pre-signals

A problem - the left train may leave first.
Solve the problem using presignals

The image on the right shows a setup where entry to a station is controlled using ordinary signals. When at least one platform is empty this works well as an incoming train is always directed to a free platform. However, consider what happens when all platforms are full as in the screenshot. All branches are showing red so the incoming train picks the easiest path - straight on. But suppose the train on that platform is going to be in the station for some time. Meanwhile the other train leaves. The incoming train has committed itself to a platform and is stuck waiting for a train to depart even though there is now an empty platform available! We need to stop that incoming train having to make a decision between two red signals. For this, we need to use pre-signals.

Pre-signals are signals that decide on which colour to show not only by the status of the track immediately beyond, but also by the status of other pre-signals further down the line. Specifically, a pre-signal shows a green light if, and only if, there is a green exit from the block behind it. You as the planner need to identify which signals are to be the pre-signals and which are to identify exits.

Entry Pre-signals

Entry presignal.png
An entry presignal shows green as long as there is at least one green exit signal on the following section of track. Otherwise it shows red. This prevents trains from entering the signal block until there is an available exit. Note that depots have a built-in two way signal (it works as an entry pre-signal in a pre-signal set).

If there are no signals designated as exits behind the entry pre-signal, it behaves as a normal signal. This is convenient for bi-directional presignals where only one direction needs presignal functionality.


Exit-signals

Exit presignal.png
An exit signal behaves in the same way as a normal signal but is necessary to trigger the correct colour on entry and combo pre-signals.


Combo-signals

Station with 1 entry pre-signal, 2 combo-signals, and 4 exit-signals
Combo presignal.png
There is a third type of presignal that doesn't really introduce any new functionality. It is called the combo signal and simply acts as both an entry and exit signal. This allows you to build large "trees" of presignals as shown on the right.


Building Presignals

To build presignals, first place an ordinary signal. Then, with Ctrl held down, click the signal to cycle through the different kinds of presignal.

Note that you can build one way pre-signals in the same way as you build ordinary one way signals. Remember: holding Ctrl and clicking toggles the type of (pre)signal, clicking without Ctrl changes the direction of signalling.

Remember not to hold down Ctrl when placing the signal initially or you will end up with a semaphore (see below).


Limitations

The problem with presignals...

An important point to note with exit signals is that a green exit signal will trigger a green on the entry pre-signal at the beginning of the block even if it is not actually possible for a train to get to that exit signal because of the track layout (as in the image to the right with a train entering on the bottom track). This can ruin more complicated presignalling setups so care needs to be taken with planning.


Path Signals

NightlyIcon.png

Nightly Builds
The features mentioned in this section are currently only available in non-production releases such as nightly builds, betas or release candidates.

Two new signal types in the signal GUI.
YAPP adds two new signal types to the game. These signals enable trains to reserve a path through a signal block before entering the block. If another train wants to enter the block, and succeeds in reserving a path through the block, both trains can use one signal block at the same time.


As mentioned before, there are two signal types, available in the Signal GUI. The first type is the basic Path Signal. There are two things you should know about this signal:

  • Place it only where trains can stop and wait safely without blocking junctions and other things.
  • Trains can pass through this signal from the back side.
Path Signal
This signal will be called a Path Signal.


There are also two things you should know about the second signal type:

  • Place it only where trains can stop and wait safely without blocking junctions and other things.
  • Trains can pass through this signal from one direction.
One-Way Path Signal
This signal will be called a One-Way Path Signal.


Most of the times it will be sufficient to use a default Path signal, as passing a signal from the back is penalised by the pathfinder, however, one-way Path signals might be useful in certain specific cases.


The two new signal types behave a bit different than standard OpenTTD signal types. The Path signals are red by default, and will only show green as soon as a train can reserve a path to the next safe waiting position on its route. Safe waiting positions are - by definition - in front of signals, depots and track ends. The back of a Path signal is not considered a safe waiting position, and therefore paths are reserved through these signals.

Because the front of every signal is defined as a safe waiting position, you would normally not want to place a signal immediately behind a junction, only in front of a junction. This is because it is only safe for a train to wait in front of a junction. It is not safe for a a train to wait at a signal immediately after a junction before the whole train has cleared the junction, as it would be blocking the junction while waiting, as illustrated in the example below. This is a major advantage against standard OpenTTD signals, where you had to place signals before and after junctions, which caused trains to block junctions while waiting.

The signal indicated by the arrow is an unsafe waiting location, as the train in the junction now blocks the otherwise free path of the train coming from the top. There's a second unsafe waiting location in this picture. Can you find it?

Patch Options

YAPP Patch options
YAPP adds three patch options to the game.


One option is to highlight reserved PBS tracks. This option is useful to troubleshoot your PBS junctions, as you can see what paths trains have reserved through a PBS block.


The other two options control how the build signal tool should behave. You can set the signal type which should be built by default when building a new signal with the signal tool and change which signal types should be cycled through on ctrl-clicking an already existing signal.


There are a few more patch options which are not available through the Configure Patches windows. What these options are, and how to edit them is covered below under Advanced Options & Features.

Basic Examples

Below are some example track layouts which use the YAPP-PBS signals. Advanced track layouts that are not recommended for beginners can be found here.

Basic junction

This basic junction now has a much higher throughput.

Basic junction for trains with maxlength three tiles. Note the use of normal signals on plain track.

Basic two-way station

With this station layout, trains can use both platforms when coming from either direction.

Basic station.

Semaphores

Semaphore.png

Semaphores are a type of signal with no functional difference from regular signals. They simply have a different (old-style) appearance.

Before OpenTTD 0.6.0 semaphores were only created by holding Ctrl while placing the signals. Since 0.6.0 semaphores will be created instead of light signals before a configurable year, 1975 by default. This setting is called "Automatically build semaphores before" and can be found in the "Advanced settings" under "Construction" and then "Signals".

After placement, holding Ctrl and clicking changes the extended signal status of the signals (i.e. presignals). You can change pre-placed semaphores to light signals by choosing the "convert signal" tool from the signal-gui and ctrl+clicking on an existing signal.

History

Semaphore signals have a long history in rail lines. Long before the advent of electric lights, Semaphores were used to indicate the direction of switch-tracks, and the safety of going into the tracks beyond. Semaphores are simply mechanically controlled signs that raise or lower based upon the status of the track.

In the original Transport Tycoon, rail signals created before 1975 were semaphores. Afterwards, signals were created as standard coloured lights. Transport Tycoon Deluxe removed this functionality, but it has been restored in TTDPatch and OpenTTD.

As of v.0.6.0 (or thereabouts) OpenTTD places semaphores by default. There is a patch option to change this.

Directing trains

Note that signals are not the best way to direct trains to completely separate destinations (just to prevent them crashing and help them choose between several track sections to the same destination). If you want to do that, you should use Waypoints.

See Also

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