User:Timitry/Junctions

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Railway junctions
Tutorial: Junction basics | 3-way basics | 4-way basics
Advanced junctions:
3-way: 1-track sideline and 2-track mainline | Example 2 | Example 3
Example 2 | Example 3
Example 2 | Example 3


Contents

Introduction

Railway junctions are formed when one piece of track meets another one, and can vary greatly in size, trainspeed, connected tracks and throughput.

This tutorial will show you the basics you need to know to build your own junctions. It is recommended that you activate realistic acceleration, or else your trains will slow down massively at hills. Always keep in mind that there is not one perfect junction - different situations require different junctions!

Important basics

Block signals versus path signals

Block and path signals before doubled bridges

Since the 0.7-branch of OpenTTD, you can choose between building block and path signals. If you want to learn how the different kinds of signals work, have a look at the signals page.

One can't really say which of the two kinds is better, they both have advantages and disadvantages, and a lot depends on personal taste. However, there are situations where one kind works better than the other one. Especially on simple junctions, where tracks cross each other, path signals often provide a higher throughput since they allow more than one train on the junction, for an example see the basic 3-way junction.

On advanced junctions, you will probably not have crossing tracks at all, and so the difference between path and block signals is only very small. Most of the time you can only save a tile or two by using path signals rather than block signals on these junctions, like illustrated in the picture to the left. However, block signals offer the possibility of creating priorities and other complex constructions. Since you can mix both kinds, you can always decide which to use and don't have to make a definite choice.

Actually, the picture on the left illustrates a perfect example of _bad_ PBS, the block signal version is much more efficient (shorter signal gap) and it only cost you one single tile //Aali

Trains can go in any direction

Usually junctions are build in such a way that a train coming from one direction can go to each possible direction. Providing a possibility for trains to make an u-turn is usually not needed. If you know that there won't be any trains which will go from A to B, you could leave out that connection and simplify your junction, just remember that there is a missing connection!

Signalling distance

In order to let your trains drive as close to each other as possible, you should consider placing signals each two tiles. Placing them each tile does not have great benefits, since you can't place them on tiles where the track splits or merges. Placing them less then each two tiles will decrease the throughput of your tracks and junctions, but if you like to play like that, it's your choice and neither right nor wrong!

Build your curves wide (enough)

With realistic acceleration being enabled, the speed of your trains in curves is limited to certain values. A good explanation is given here. Before starting the construction of your junction, you should find out which curve radius you need for your trains to drive through them at maximum speed, considering their length and maximum speed. If you try to rebuild a junction you see on a screenshot, you should always expand or shorten the curves so that they fit your actual needs. Of course you can build curves which your trains can not use with maximum speed, but those should not be situated at a very busy piece of track. However, try to avoid 2x45° turns (just one piece of diagonal track for the curve) all the time!

Climbing hills

With the use of realistic acceleration, trains will not slow down when climbing a small hill and having enough power, so don't hesitate to build bridges or tunnels. However, they might still slow down if climbing a huge slope, depending on their power, so try to avoid these if you fear that your trains might get stuck!

Speed limits

While trains can always use tunnels with their maximum speed, bridges have speed limits. Try to ensure that your trains can use all bridges at maximum speed, and if that is not possible, try to build tunnels instead!

Split tracks before merging

Merge before split
Split before merge

When building junctions, you should try to always split tracks before merging them. An example why you should not do it the other way around is provided with the picture to the left: The train leaving the straight track blocks the other train, which wants to join that track. If you split tracks before merging them, like shown in the picture to the right, that problem is solved and neither of the trains has to wait for the other. Using merges before splits can even cause gridlocks, which often won't solve themselves but need your interaction. Building the splits before the merges might often be more complicated, but it is worth the effort!

Provide enough space for waiting trains

Waiting space

When merging tracks, it often happens that one train has to wait for another one to pass. The waiting train could possibly block the train behind it, which might want to go another way. If you have the space, try to ensure that a waiting train fits between the split and the merge, like in the picture to the left: Even though the train in the middle has to wait, the train to the left can still continue driving straight over the bridge.

Safe waiting positions

The train turning left is blocking the junction
With safe waiting positions, the train does not block the junction anymore!

The following only applies to path signals, not to block signals! When designing junctions using path signals, you might want to provide safe waiting positions for your trains. You can do that by not constructing the first signal after a junction as close as possible to it, but rather as far away as to leave enough room for the longest train using the junction to completely fit between the signal and the junction. If one of the lines going away from the junction is jamming up, a train waiting for that jam to solve will not block the junction for trains going to other directions. However, the disadvantage of safe waiting positions are that they decrease the throughput of your junctions since they increase your signal distance. There is no definite recommendation whether to use them or not, beginners might be better of using safe waiting positions, while players using advanced junctions will not need them in most cases.

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