In addition to the standard signals from the original TTDX, there are now several new signal types, some only available in TTDPatch, others only in OpenTTD. They all offer new functionality and can solve certain problems, but also lead to new headaches, if their functions are not completely understood. This page introduces the various signal types, detailed explanations are given on extra pages.
standard signals
Standard signals show "Stop!" if there is a train in the signal block behind them. Thus there can only be one train in a signal block at any given time, which prevents any collisions. The behaviour of these signals is rather easy to understand, however they are also quite limited when it comes to complex signalling tasks.
Usage
The only useful task left for them is the forming of signal blocks on rails which should be used in only one direction. The principle of such a block is the base for doubletracked networks and is explained there in detail.
pre-signals
Presignals were the first new signals that have been introduced. The main goal was to solve problems with station entries, which was not possible with the standard signals.
There are three types of presignals: Entry, exit and combo, with the combo signal being a combination of entry and exit. The criteria for these signals to show "Go!" or "Stop!" are a bit more complex and are explained in detail on an extra page.
Usage
By now these signals are only interesting for very specific tricks. Path-based signals and other new signal types in TTDPatch offer much more functionality. Path signals in OpenTTD are much simpler to understand and offer a more flexible approach. So, presignals have become almost obsolete.
path signals (TTDPatch)
Path-based signalling was kind of a groundbreaking feature, as it enables the player to built realistic, small and yet effective junctions. Using these signals is comparably complex and is discussed on an extra page.
Usage
Just about everywhere, especially where more than one train should be in a signal block because otherwise jams would easily occur. Path signals are most useful in areas like station entries or on complex junctions where many trains have to go through.
Restrictions & Programmable Signals (TTDPatch)
Routing destrictions are a very powerful and rather complex feature that can be used to control train movement in a manner not possible before. It influences train pathfinding by setting user-defined restrictions upon signals. The route finder does not search for a way past a restricted signal if the train does not meet the restriction criterion. In other words, the restriction discourages the train to go to the signal if it does not meet the restriction criteria. This can be used to route a train with a certain freight or speed onto a specific track.
Programmable signals allow almost complete control over signal behaviour. The player creates a rule or a set of rules which determine when the signal should show "Stop!". These rules work in addition to the standard behaviour of the underlying signal type, which means you cannot create a signal that permits passing into a block thats occupied by another train.
Because of the huge complexity and the amount of possible settings tehre is an extra page with detailed explanations.
Usage
Routing restrictions are very helpful to control train movement when they should only use certain tracks. This could be done by waypoints of course, but sometimes there is no room for them. Programmable signals can be used to combine the useful features of presignals and the advantages of path signals - path signals override the pre-signal behaviour by default.
Through signals (TTDPatch)
In real networks, trains can often switch onto the "wrong" lane (the one for the opposite direction) in order to overtake slower trains. This behaviour could not be simulated in TTDX, now with these through signals it becomes possible. Using the signal GUI, one-way signals can be converted. This will also promote the signals to PBS ones, so PBS needs to activated to use these signals. It has no impact on two-way signals, since they obviously allow bi-directional travel.
Usage
These signals are useful at every place where trains need to get to a certain track from both directions (for example at a station). Without through signals two trains could try to enter a track at the same time, leading to jams. The pages about stations show examples. An example for changing the tracks on a double track line is shown in the section about double tracked networks.
Inverted Routing (TTDPatch)
One-way signals differ from two-way signals concerning their impact on routing. In short, two-way signals propose a choice among various alternatives, while one-way signals tell the train that he has to take this track and no other to reach its destination. However, there may be situations where you need to have two-way signals without allowing a choice among various signals. That is the point where this feature becomes quite handy, since it tells the pathfinder to treat one-way signals as two-way and vice versa.
Usage
There is exactly one spot where this signal is extremely useful: At the entrance to stations, where trains should not turn around and where this would be possible due to the game options. This problem is discussed in detail on the page about through stations.
path signals (OpenTTD)
YAPP stands for Yet Another Path-based signalling Patch and implements path-based signalling in OpenTTD. This implementation has thrown away several limitations of the older signal types, leading to a very simple and elegant solution, which can solve just about any signalling problem. There is an extra page for the detailed introduction.
Usage
Always and everywhere! Especially for newcomers to the game, path signals are much easier to understand, because one does not have to mess around with the various pre-signals types.
