Junctions are formed at any point where a piece of railway track directly crosses or joins another piece. In OpenTTD, references to junctions are almost always talking about rail junction because the other modes of transport either do not need them or they are trivial to build.
In practically all cases, signals are required in order to prevent trains crashing. Junctions can range from very simple to very complex, depending on the number of tracks to be joined, the direction the trains are to travel and the number of trains expected to use the junction at any one time.
Track layouts contain no merging or spliting of the tracks.
Tips for building junctions
- Sharp corners slow down trains. Use at least a one-tile track segment between 45° turns; longer is better.
- S-shape bends do not slow down trains.
- Climbs slow down trains greatly, unless you are using the realistic acceleration patch. Avoid ramps on the most important lines in the junction.
- Bridges that are less than 4 track segments long (from start to finish) have lower speed limits. To avoid this, make your bridges at least 4 tiles long
- Tunnels do not have speed limits.
- Gridlock can happen in junctions that have merges before exits. Try to make the merges after the exits.
- Trains that have to wait for another train to pass before it can merge can cause traffic jams. Try to make each exit branch longer than your trains.
Design tips to consider before building a junction
- The most efficient junction is no junction at all.
- Even the best junction means a potential delay for your train if its path is blocked. This kind of delay doesn't happen if trains that go to different destinations have completely separated tracks.
- Some conditions may force you to reuse existing track nevertheless: prohibitive costs of building or maintenance (as seen on some multiplayer servers) and constrained space (which happens very rarely except on really small maps).
- Build as few directions as possible.
- Every additional direction means you have to cram more track into a constrained space, which means sharper turns and more bridges and tunnels.
- If for example, you want to connect 3 coal mines to a single power plant, you don't need to build a 4-way junction; three separate line merges will work far better.
- Build only those directions that are actually going to be used. Not every junction needs to have any exit accessible from any entrance.
- Unused paths take precious space, which can be utilized for gentler turns on the paths that are actually used.
- In the above example of 3 coal mines connected to a power plant, there will be no traffic between the coal loading stations, which means that these stations don't have to be accessible from each other.
- Plain stretches of track are boring.
- Build epic junctions just for the sake of it! Show off and have fun!