Contents
• Through signals
• Inverted routing

TTDPatch introduced two new types of signals, which try to solve specific problems related to restrictions from the original TTDX game.

Through signals

All signals in the original TTDX and in TTDPatch can only be passed from the correct side. In reality, regulations usually state that signals facing the opposite direction are to be ignored and have no influence on the train. In certain situations in the game, it can be beneficial or even necessary to do that as well, so these signals were introduced.

In OpenTTD, one-way path signals are already defined in such a way that they are ignored when facing the opposite direction. That means they act like these through signals by default.

In real networks, trains can often switch onto the "wrong" lane (the one for the opposite direction) in order to overtake slower trains. This behavior could not be simulated in TTDX, now with these through signals it becomes possible.

Using the signal GUI, one-way signals can be converted to through signals. This will also promote the signals to path based ones, so the path-based signalling feature 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

These signals solve a problem that is inherent to the way the pathfinder works in the original TTDX game: Whenever a train has multiple choices to continue its journey, all ways marked by a two-way signal are treated as equal alternatives, whereas a one-way signal tells the pathfinder that only this track is the one to continue on. This distinction is relevant for example at station entries, when all choices going to the platforms should be treated as equal, while diverging lines to different stations should not be treated as equal choices.

Inverted signals flip the type of signal for the pathfinder to the opposite, meaning a one-way signal is then treated as an equal choice, while the two-way signal is not.

OpenTTD uses a completely new pathfinder algorithm which does not use this distinction. This problem therefore does not exist and no specific signal to circumvent it had to be created.

There may be situations where you need to have two-way signals without allowing a choice among various signals. The best example are through stations in which a train might turn around and leave in the wrong way after loading.

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. Apart from that change in the pathfinder, the type of signal, e.g. block signal or presignal, stays the same.

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.