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.