Signals

From OpenTTD

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 1 Signal Construction 2 New Signal GUI in 0.6.0 3 Two-way signals 4 One way signals 5 Pre-signals 5.1 Entry Pre-signals 5.2 Exit-signals 5.3 Combo-signals 5.4 Building Presignals 5.5 Limitations 6 Semaphores 6.1 History 7 Directing trains 8 See Also

[edit] Signal Construction

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 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.

[edit] 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)

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.

[edit] Two-way signals

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.

[edit] One way signals

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 its direction track as if there were no signals (i.e. it does not take any notice of the colour a signal is showing). 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.

[edit] Pre-signals

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.

[edit] Entry Pre-signals

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.

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.

[edit] Exit-signals

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.

With NPF disabled, exits should normally be two-way signals, so as to give the train a choice. With one-way signals and no NPF, the train would be permitted to pass the entry signal as normal as soon as one of the exits cleared. However, it would then pick exit to the shortest path to its destination, which would not necessarily be a green signal!

NPF lifts this "restriction" and trains will choose the least cost path to their destination. Red signals have a higher cost than green, so trains will not wait at them if it can be avoided.

[edit] Combo-signals

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.

[edit] 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).

[edit] Limitations

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.

[edit] Semaphores

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".

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.

[edit] 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.

[edit] 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.

[edit] See Also

• Examples of advanced presignal setups
• Advanced Main Line Depot
• Category:Train Junctions for examples of complex junctions that take advantage of pre-signals.