Why should one bother with building a complicated network with tons of signals and stuff? This question is asked by most newcomers to the game. The answer is rather simple: You will run out of space for building a dedicated track for each train. And with a simple double tracked line it is easily possible to have more than a dozen trains running on it. When having to change a connection or add access to the next factory, this becomes much easier compared to building a whole new connection. In the long run, you save lots of money that can be invested in vehicles (aka moneymakers).
There is one disadvantage, though. Trains in badly designed networks might get lost or block each other. But these problems can easily be circumvented when keeping some simple basics in mind when building the network. And that is what this page is about.
Single line
Single line setups are the cheapest way to connect two stations. As the name suggests, there is only one track which is used in both directions. On such a line exactly one train can travel, for more trains you need - surprise, surprise - switches and signals.
This most simplistic form can only handle one train that travels between both stations. Between both ends of the line additional stations can be built, but as long as they do not have more than a single platform and appropriate signalling, the capacity of the line is still limited to a single train.
This setup allows two trains to run. One waits at the station on the right, the other one is on its way between the stations.
The signalling is the same as in the original TTDX and uses two-way block signals.
This setup can be used by three trains. Two trains are waiting, one at each station, and the third one travels between both stations. This system only works with PBS, because this does not allow trains to go towards a two-way signal showing "Stop!". Without PBS it could happen that both platforms are used and a third train approaches the station, blocking the line because it cannot enter the station.
By reserving the paths it will also (at least for three trains) alternate between trains going back and forth: Assume that there are two trains in the station on the left, the third one in the station on the right. That means one of the two trains from the left has to go the right, as there simply is no other possible way. Afterwards, a train from the right hand side has to go to the left, as again only that station has a free track to go to. The tree trains therefore always switch back and forth.
This setup can be expanded, with each new platform allowing one more train. However, as the connection between the stations remains a single line, this is not very useful as trains would wait for a green signal most of the time. It is much more useful to add passing places.
Shared tracks
Usually, lines will meet at stations, or there are parts which will be used by several trains together. It is necessary to place the signals correctly for this to work, as shown in the next images.
Both lines to the left and right share the central track. The two-way signals make sure that only one train can use this central section, separating it from the rest of the line. However, this only works for two trains, one per line!
Instead of sharing pieces of track, trains can share a station just as well. Signalling works in the same way. Of course, there is still the limit of only having one train per line, so two trains in total.
One-track lines can also share larger stations. Still, only one train per line is allowed, so that the tracks leading away from the station are not blocked. In this setup, three trains can be used. This would also work without path based signals, but it would be less efficient.
The layout of multiple one-track lines sharing a station can be extended easily, either by adding further one-tracked lines, by adding tracks to a line, or by enlarging the station.
Passing places
Bigger stations at the end of the line do not help much to raise the capacity of the line, as long as trains cannot pass each other outside the station. To make this possible, passing places (sidings) have to be built.
This is how a track with a passing place looks in principle: a one-track line connects the two stations, in the middle there is a double-tracked section (the signals have been left out here on purpose, this will be discussed in the next sections). To make the passing place work, the tracks there have to be long enough to fully accommodate any train traveling on the line, so that they do not block any switch tile when waiting. With such a passing place on the line, two trains can use the line, one on the single-track section to the left, the other one on the right.
You also have to be very careful about signalling here: If trains can block each other at a passing place, they eventually will do just that, forcing the player to manually solve the problem. Still, this can be prevented by adhering to a simple rule:
So how can the rule stated above be fulfilled? There are different options with different signal types, but the only solution that is guaranteed to work is the usage of path signals.
The two path signals regulate traffic at the passing place. A train reserves a path to the signal at the end of the passing place. As soon as it enters the passing place, the track behind it becomes available, a train waiting to go in the other direction can now reserve the track and start its journey. A train following the first one will have to wait until the first train has left the passing place, as this makes the path available for reservation. This guarantees that train cannot block each other.
For longer single-tracked lines one can build multiple passing places. Each of them needs to be built in the same way and with the same signal layout. The maximum capacity of the line is then equal to the sum of single-track sections between the passing places: In each such section exactly one train can travel.
Instead of having tracks in a passing place, one could also build a station there. One can also increase the size of the passing place / station by adding further tracks to the left and right and placing the signals in the same way for the corresponding driving direction. However, increasing the size is not that useful, one should rather add a second track to the line.
Shared tracks revisited
As already briefly discussed in the part about one-tracked lines, adding passing places into the setups might require some changes to signal placing. The examples from above are repeated here with explanations what has to be changed.
When sharing one-tracked lines or stations the two-way signals which separated the different lines have to be removed. Their task is taken over by the signals in the passing places. Trains now always reserve the whole track, including the parts that are shared with the other line.
If there is a station at the end of a single-tracked line and there are passing places before that part, one needs to place a two-way signal in front of the station. Without this signal the path reservation runs into problems, since trains can only correctly reserve a path from the passing place into the station. The way back is only reserved after the train has reached the station. However, it might happen that the passing place is already in use, so that the train cannot reserve a path from the station to the passing place. So in order to prevent crashes, the game will stop the train there, forcing the player to solve the problem. The two-way signal at the station solves the problem, enabling the train to reserve the paths properly, and when no path out of the station is available, it will wait at the signal.
Sharing stations between several single-tracked lines with each being used by more than one train also requires slight changes in signalling. The signals at the station stay the same, but the ones at the single-tracked line are removed, their task is taken over by the signals at the passing places.
Shared tracks revisited
For large-scale tasks (meaning many trains), single tracks are not enough, because of the increased interference of trains with each other. The capacity of a track that is used in both directions is just too small. The solution is simple: One dedicated track per direction. This will result in two tracks and huge capacities or just about any task. Most railway lines in the real world are built in that way as well.
This is the standard double-tracked line. Noteworthy are the path signals placed in regular distance (one can also use block signals instead, it would not change anything about how the line works, but just placing path signals everywhere on the network makes things much simpler).
These signals act as automatic signal block (that's the term in the real railways) and increase the line capacity. The closer these signals are placed, the sooner a train can follow, and the more trains can run on the line in the same time. In reality, signals are placed several kilometers apart, in the game a distance of about three tiles is usable very well.
Double-tracked lines have enough capacity for most tasks, even with many trains running on them. In order to create a well-working network, well-working junctions will have to be used. This topic is rather complex, therefore it is discussed on an extra page about junctions and crossings.
In real networks, trains can often switch onto the "wrong" lane (the one for the opposite direction) in order to overtake slower trains. This can also be done in the game, although one should only try it on lines with not too much traffic, because that would only lead to train blockages. This system is especially useful if the trains have a huge difference in speed, i.e. for express trains overtaking slow freight trains.
When building switches for the trains to switch tracks one should take care that trains cannot change their direction by doing a 180 degree turnaround - that is unrealistic and can wreak havoc with the traffic on the line. Usually it is a good idea to turn of the feature that trains can run across 90-degree corners anyway.
To allow switching the track one has to use signals which can be crossed in both directions and which allow reserving paths in such a way that a returning onto the correct track is simply possible. This is only possible using through signals. The layout shown here is just one possible solution, it has the advantage that trains cannot turn around, preventing them from getting lost.
This switching of tracks does not work well on busy lines, as oncoming trains will prevent trains from "overtaking" - same as on a busy road where it becomes almost impossible to overtake as there are always oncoming cars. A solution for such busy lines are dedicated overtaking sections with additional tracks. Their setup and how to do the signalling for it is described in overtaking sections.