How switching works?
December 22, 2020
Switching happens when a train has multiple possible paths when going to a waypoint.
The game automatically creates a switching signal at the place where a switching decision is made:
When a train arrives at a switching signal, it must decide which path it will take.
For that, it inspects the different signalling blocks:
– the switching block is the block just after the switching signal
– the outgoing blocks are the blocks just after the switching block
Here are the rules for switching:
– If the switching block is occupied, the train waits at the switching signal.
– If not, the train inspects the outgoing blocks and chooses one that is not occupied.
– If all the outgoing blocks are occupied, the train waits at the signal.
In our simple example, in this situation, the train will choose the upper path, because the switching block and the upper outgoing block are not occupied :
In this situation, however, the train will choose the lower path, because the upper outgoing block is occupied:
In this situation, the train will wait because all the outgoing blocks are occupied:
That’s it! Switching is quite easy when you know the rules.
For successful switching, you have to be careful how you place your signals though.
Let’s have a look at some common design errors:
Missing signalling blocks
In this situation, the switching will never happens, because there is no signals, and therefore no signalling blocks to inspect.
In this situation, the switching will not happen either. The incoming train will always wait at the switching signal, even though the second platform is available. The reason: the tail of the long train on the station platform is blocking the switching block.
For long trains, you must use stations with long platforms. See the Railropedia to learn how to do that.
This one is a bit trickier. Can you see what is missing?
In this situation, the switching will never happen. The outgoing blocks are incomplete: there are signals at the station entries, but not at the exits. As a result, the two platforms form a single signalling block.
Wrong outgoing blocks
In this situation the incoming train will not go the lower track. It will go the the upper track even though the upper platform is occupied. Can you see why?
In this case, the outgoing blocks used to decide the switch are not the station platforms. They are the tracks just after the switching blocks and they are both empty. So the train will take the upper path, and will queue behind the loading train.
Sometimes, this is what your want, but if not, make sure you know which blocks are used to decide the switch.
Sometimes a block is bigger than you think.
In this situation, the two outgoing blocks are connected by a crossing track. They are merged and form a single block. As a result, the switching will never happen.
In this network, the player connects two stations with two tracks. The player hopes that trains will switch at the first rail switch, choose an empty track, then switch at the second rail switch to find an empty platform.
But it does not work. Trains always end up facing each other.
Do you see why?
Things get clearer when you display the train paths:
The router will always look for the shortest paths. In this setup, this means that trains will switch only once between A and B, not twice. The second rail switch is never used.
Rail switches do not matter for train switching. Only the actual train paths are considered.
Balancing traffic between two bi-directional tracks is very difficult. A possible alternative here is to use one-way tracks instead. For this, you have to add intermediary waypoints on the tracks.
See the Railropedia/One-way tracks article for an example.