Signalling

Signalling features

• Routefinding restrictions
  Routefinding restriction programs can be attached to any kind of signal.
  These programs are run by trains, and can check various train properties, and slot and counter values.
  These programs can be used to control pathfinding, PBS, slots, counters, reversing, speed restrictions and other miscellaneous operations.
• Programmable pre-signals
  Programmable pre-signals are combo pre-signals, with programmable conditions for whether the signal is red or green.
  Programmable pre-signals are block signals, with no support for PBS.
• Slots
  Slots are analogous to token systems used in real-life railways, in particular single-line sections.
  A slot has a capacity, the number of trains which can be in the slot/have a token.
  A train can be a member of any number of different slots at once (have any number of different tokens at once).
  Trains can acquire or release membership of slots (acquire or release tokens) at signals, or using conditional orders.
  Slots can be used in conditionals in routefinding restrictions and programmable pre-signal programs, and in conditional orders.
• Counters
  Counters are named variables which can be modified when a train passes a signal.
  Counters can be used in conditionals in routefinding restrictions and programmable pre-signal programs, and in conditional orders.
  In most cases, slots should be used instead.

Routefinding restrictions

Routefinding restriction programs can be attached to any kind of signal.
These programs are run by trains, and can check various train properties, and slot and counter values.
These programs can be used to control pathfinding, PBS, slots, counters, reversing, speed restrictions and other miscellaneous operations.
Routefinding restrictions require using the YAPF pathfinder for trains.

By default, electric signals with a routefinding restriction program attached have a blue signal post.
This does not apply when using custom signal graphics, unless the "Show restricted electric signals using default graphics" setting is enabled.

Programs are executed in order from top to bottom.
In the case where one action cancels another, the last executed action takes effect.

Example 1: Combined bay and through station

This is a possible way to implement a combined bay and through station.
The example assumes that only bay-platform traffic calls next at "Southerly Station", which is to the south-east.
The two signals in front of the bay platforms share the program in the upper window.
The signal in front of the north/west bound through platform has the program in the lower window.

The bay platform signals deny access if the train is entering from the back of the signal and the next order (the order after the call at New Bedtown) is not Southerly Station.
This has the effect of stopping trains which need to continue north/west from using the bay platforms.
The "train is entering from the back of the signal" test is to avoid restricting trains trying to leave the platforms.

The through platform signal adds a pathfinder penalty if the train is entering from the back of the signal and the next order (the order after the call at New Bedtown) is Southerly Station.
This has the effect of adding a penalty for trains which could use the bay platforms, such that those trains will always use a bay platforms if one is available. However if all the bay platforms are full or otherwise unreachable, it can still use the through platform, and reverse out again afterwards.

Example 2: Station with single passing track

This is a possible way to implement a station with a single bi-directional passing track.

Trains will use the platform tracks if unoccupied, otherwise if the platform is occupied and the train does not call at this station, trains will use the central track to bypass the occupied platform.

The pathfinder penalty for a station tile defaults to 800, therefore the total penalty for a 4 tile platform is 3200.
Here the same station platform penalty is added to the central track (1600 on each of the two signals).
The backwards facing signal on entrance to the central track is large enough that the platform track has a lower pathfinder cost than the central track when unoccupied.
However when the platform track is occupied but the central track is not, the central track has a lower pathfinder cost.

The long reserve action on the central track signals is to better allow non-stop trains using the central track to overtake trains currently occupying the platform.

Actions

• Deny
  The pathfinder will see this signal as a dead end, and will not look beyond the signal to find the destination.
  This can be used to prevent trains from taking a particular route.
• Penalty
  The pathfinder will add a penalty value to the cost of pathfinding past this signal.
  This can be used to fine-tune train pathfinding.
  The current suggested values in the dropdown are: small = 500, medium = 2000, and large = 8000.
• Reserve through
  PBS will not end a reservation at this PBS signal, it is as if the signal is not there at all in the forward direction.
  This action has no effect when applied to a signalled tunnel/bridge entrance or exit.
• Long reserve
  If a train makes a PBS reservation that ends at this PBS signal, a second separate reservation will be attempted starting from this signal.
  The first reservation is not cancelled if the second reservation is not possible.
  This action has no effect when applied to a signalled tunnel/bridge entrance.
• News control
  This allows turning off the train is stuck/lost news messages for trains waiting at this particular signal.

Conditional blocks

• If
  This starts a new conditional block. The contents of which are only executed if the condition is true.
• Else if
  The contents of this block are only executed if the condition is true AND none of the previous conditions in this conditional block were true.
• Or if
  The contents of this block are only executed if the condition is true AND none of the previous conditions in this conditional block were true, OR if the previous condition in this conditional block was true.
• Else
  The contents of this block are only executed if none of the previous conditions in this conditional block were true.
• End if
  This ends the conditional block.

Conditional blocks may be nested inside other conditional blocks.

When a conditional block is selected, clicking the "Remove" button removes the entire block and its contents.
Ctrl-clicking the "Remove" button removes the condition but does not remove the contents of the block.

Conditions

• Train length
  This checks the train length in tiles (rounded up).
• Max speed
  This checks the train's maximum speed.
• Current order
  This checks the destination of the train's current order.
• Next order
  This checks the destination of the train's next order after the current order.
• Last visited station
  This checks which station the train last visited.
• Cargo
  This checks whether the train can or can't carry a particular cargo.
• Load percentage
  This checks the current load percentage of the train.
  (Trains with no cargo capacity at all are considered full: 100%).
• Entry direction
  This checks which side the train is entering the signal from: front, back, compass direction, or entering/exiting tunnel/bridge.
• Train group
  This checks whether the train is in a particular group.
  This works with nested groups.
• Train owner
  This checks which company owns the train.
• Train status
  This checks the current status of the train, the statuses which can be checked are:
  • Empty
  • Full
  • Broken down
  • Needs repair
  • Reversing
  • Heading to station or waypoint
  • Heading to depot
  • Loading
  • Waiting
  • Lost
  • Requires servicing
  • Stopping at station/waypoint
• Weight
  This checks the train's current weight.
• Power
  This checks the train's power.
• Max T.E.
  This checks the train's maximum tractive effort.
• Power / weight
  This checks the train's current power to weight ratio.
• Max T.E. / weight
  This checks the train's current maximum tractive effort to weight ratio.
• Engine class
  This checks whether the train has at least one engine of a particular class. The engine classes are:
  • Steam
  • Diesel
  • Electric
  • Monorail
  • Maglev
• Direction of order target
  This checks which direction the tile of the train's current or next order is in, relative to the signal tile.

Advanced actions

The more advanced features below are only shown if the "Show advanced routing restriction features" setting is enabled.

• Wait at PBS signal
  The sub-actions which this can take are:
  • Wait at PBS signal
    The train waits at this PBS signal.
  • Cancel wait at PBS signal
    Cancels a previous wait at PBS signal action.
  • Wait at start PBS signal for reservation ending here
    If a train would make a PBS reservation which ends at this signal, the train will instead wait at the start signal and not make the reservation.
  • Cancel wait at start PBS signal for reservation ending here
    Cancel a previous wait at start PBS signal for reservation ending here.
• Slot operation
  See Slots section below for details of what slots are.
  The sub-actions which this can take are:
  • Acquire or wait
    Try to acquire membership in the slot, if the slot is full and the train cannot become a member, wait at this PBS signal.
  • Try to acquire
    Try to acquire membership in the slot, if the slot is full and the train cannot become a member, carry on anyway.
  • Release (front)
    Release membership of this slot when the front of the train passes the signal.
  • Release (back)
    Release membership of this slot when the back of the train passes the signal.
  • PBS end: Acquire or wait
    When attempting to make a PBS reservation which ends at this signal, try to acquire membership in the slot, if the slot is full and the train cannot become a member, wait at the start PBS signal.
  • PBS end: Try to acquire
    When attempting to make a PBS reservation which ends at this signal, try to acquire membership in the slot, if the slot is full and the train cannot become a member, make the reservation anyway.
  • PBS end: Release
    When a PBS reservation is made which ends at this signal, release membership of this slot.
  • Try to acquire (on reserve)
    This is mostly the same as the try to acquire sub-action, except that attempting to acquire the slot is only done when making the reservation, not when the train may later go past the already reserved signal.
    This distinction can be important when using realistic braking, long reservations and/or more complicated reservation setups. For example, if the slot is used to control reservations further on, then the slot shouldn't be acquired when the train goes past if another slot for a different reservation has already been acquired.
• Reverse behind signal
  The train reverses behind this signal. The signal must be a PBS signal (not one-way), and the train must be entering from the back direction.
• Speed restriction
  Set a speed restriction on the train when the train passes the signal.
  A value of 0 removes the restriction.
• Counter operation
  See Counters section below for details of what counters are.
  The sub-actions which this can take are:
  • Increase
    Increase the value of the counter when the front of the train passes this signal.
  • Decrease
    Decrease the value of the counter when the front of the train passes this signal. The value will not decrease below 0.
  • Set
    Set the value of the counter to a particular value when the front of the train passes this signal.
• Penalty config
  The sub-actions which this can take are:
  • No PBS back penalty
    Do not apply the pathfinder penalty for passing this signal from the back side.
  • Cancel no PBS back penalty
    Cancel a previous do not apply the pathfinder penalty for passing this signal from the back side.
• Speed adaptation control
  The sub-actions which this can take are:
  • Make exempt
    The train is made exempt from automatic speed adaptation when the train passes this signal.
  • Remove exemption
    A previous exemption from automatic speed adaptation is removed when the train passes this signal.
• Signal mode control
  This action may be used to override whether a reservation made from a combined normal/shunt style signal
  uses normal or shunt mode. The normal/shunt mode affects the displayed signal aspect, and the train driving
  model if the train braking is aspect limited setting is enabled.
  This action is executed after the reservation has been made.
  This requires the realistic train braking model.

Advanced conditions

The more advanced features below are only shown if the "Show advanced routing restriction features" setting is enabled.

• Train in slot
  This checks whether the train is currently a member of the slot.
• Slot occupancy
  This checks how many trains are members of the slot.
• Slot occupancy remaining
  This checks how much unused capacity there is in the slot, this is the slot capacity minus how many trains are members of the slot.
• Counter value
  This checks the value of a counter.
• Current time/date
  This checks the current time/date. The hour and minute values require that the savegame setting "Show time in minutes instead of days" is enabled.
  This is not affected by any use of the setting "Use client time settings instead of savegame time settings".
  The time values which can be tested are:
  • Minute (0 - 59)
  • Hour (0 - 23)
  • Hour and minute (0 - 2359)
  • Day (1 - 31)
  • Month (1 - 12)
• Reserved tiles ahead
  This checks the number of tiles of reservation ahead of the train (rounded down). This requires the realistic train braking model.
  This is mainly useful to control the long reserve action.
• PBS reservation passes tile
  This checks whether the train's reservation passes through the tile, at any point along its length.
• PBS entry signal
  This checks the tile of the PBS signal where the PBS reservation is starting from.
  Note: When a PBS reservation passes through a signal using the "Reserve through" or "Long reserve" actions, the passed signal does not become the PBS entry signal.
  This is mainly useful to control the long reserve, reserve through and possibly wait at start PBS signal for reservation ending here actions.
  This condition may not be used with the signal mode control action.
• PBS end signal
  This checks the tile of the PBS signal at the current end of the PBS reservation. This requires the realistic train braking model.
  Note: When a PBS reservation passes through a signal using the "Reserve through" action, the passed signal does not become the PBS end signal.
  Note: When a second PBS reservation is started at a signal using the "Long reserve" action or due to the train reserving ahead, the signal does become the new reservation end signal.
  This test should be used when checking which signal is used to enter a block when using realistic braking, not PBS entry signal signal, which could return a signal closer to the train.
  This is mainly useful to control the reserve through and possibly wait at start PBS signal for reservation ending here actions. This is not useful for controlling the long reserve action.
  This condition may not be used with the signal mode control action.
• PBS reservation end tile
  This condition may ONLY be used with the signal mode control action.
  This condition checks the tile at the end of the reservation (the last reserved tile), after the reservation has been made from this signal.
  This requires the realistic train braking model.

Note that the PBS entry/end signal conditionals are somewhat tricky to use and can have non-intuitive behaviour when used with pathfinding/penalty actions, because pathfinding also takes place beyond the current signal block where any reservation is being made. In this case a prediction of what the PBS signal would be is made.

Programmable pre-signals

Programmable pre-signals are combo pre-signals, with programmable conditions for whether the signal is red or green.
Programmable pre-signals are block signals, with no support for PBS.
Programmable pre-signal programs cannot test any properties of trains, and are run even if there is no train approaching the signal.
In most cases, routefinding restrictions are more useful.

Unlike routefinding restrictions, programmable pre-signal programs end when the first "Set signal state" line is reached.

Programmable signals are not shown in the signal window by default, "Show programmable pre-signal feature" must be enabled.

Slots

Slots are analogous to token systems used in real-life railways, in particular single-line sections.
A slot has a capacity, the number of trains which can be in the slot/have a token.
A train can be a member of any number of different slots at once (have any number of different tokens at once).
Trains can acquire or release membership of slots (acquire or release tokens) at signals, or using conditional orders.
Slots can be used in conditionals in routefinding restrictions and programmable pre-signal programs, and in conditional orders.

Slots are not shown in the user interace by default, "Show advanced routing restriction features" must be enabled.

Slots can be created, deleted, renamed, have their capacity changes, and have trains manually added/removed from the slot by selecting "Manage slots" in the train list window "Manage list" dropdown.

Road vehicles, aircraft and ships can also use slots. These can only use conditional orders to check and control slot membership (not signals), but otherwise function the same as train slots. Each vehicle type has a separate set of slots.

Example 1: Using slots and pathfinder deny to hold trains in queuing sidings

In this example, only one recycling train should be full-loading at the station at a time.
Other recycling trains may be held somewhere more convenient some distance away from the station until it is free.

At the first, right-most signal, recycling trains headed for the station try to reserve the slot.

At the second signal, recycling trains which are not in the slot (they did not manage to acquire the slot) may not pathfind past the signal.
This forces them to pathfind via the adjacent queuing sidings.

At the siding exit signals, recycling trains wait indefinitely until they can acquire the slot.

At the platform exit signal, if the train is leaving the platform (entering the signal from the front), the slot is released, allowing another train to acquire it.

The slot is shown in the slots management window as 1/1, this means that it is occupied by 1 train and has a capacity of 1, it is currently full.
The train occupying the slot is shown on the right, this is the train currently in the platform.

Example 2: Using slots and conditional orders to divert and hold trains in queuing sidings

This example is similar to example 1, except that conditional orders are used to divert trains which cannot acquire the slot into the queuing sidings.
This is useful when the train would not otherwise go past the sidings, such that it would be impractical to divert the train into the sidings using pathfinder deny or penalty routing restrictions on signals.

After passing the waypoint at order 16, the conditional order at order 17 is evaluated.
If the train is already in or can acquire the slot, the train immediately jumps to order 21.
This bypasses the orders for the queuing siding, such that it need not go near the sidings at all.
If the slot is already full and the train cannot acquire the slot, the train immediately proceeds to order 18.
This diverts the train into the siding via another reversing siding.
The train is held in the siding by a routing restriction on all the siding exit signals which waits until the train can acquire the slot.

See above for a diagram of the positions of orders 16 to 21.
Using conditional orders in this ways allows more flexible placement or selection of queuing sidings.

Example 3: Using conditional orders and slots for dynamic dispatch of trains

In this example a single set of trains with shared orders services multiple producing stations.
When one of the producing stations has more than a threshold quantity of cargo waiting, a single train is dispatched from the sidings to that station.
(Alternatively a depot or station could be used instead of sidings).
Each producing station has an associated slot of capacity 1. This is to ensure that only one train at a time is dispatched to each station.

This allows using fewer trains than there are loading stations to be serviced.

For each of the producing stations:

1. Use a conditional order to check whether there is enough cargo waiting at the station, if not skip this station.
2. Try to acquire the slot for this station, if not (meaning that another train has already been dispatched there) skip this station.
3. Go to the producing station and load cargo.
4. Release the slot for the station.
5. Go to the accepting station and unload cargo.
6. Return to the sidings.

The train will not move from the waiting sidings waypoint/depot/station if there are no stations available to load from such that the conditional order jumps lead to the order for the waypoint/depot/station where the train is already waiting.

NB: It is strongly recommended that a timetabled wait time is added to the sidings waypoint, depot or station order where the train waits.

Example 4: Bidirectionally signalled lines

In this example a single track line is signalled in both directions.
Multiple trains can travel in the same direction on the line at once.
Slots are used to avoid a deadlock where trains travel in opposite directions on the single line at the same time and block each other.

One slot is required for each direction. Each slot should have a capacity at least as large as the number of trains which could be travelling in the same direction at the same time.

Here two trains have entered the single line heading north. Both trains acquired the northbound slot, such that the occupancy of the northbound slot is two, and the southbound slot is empty.

If the southbound slot was not empty, the trains would wait at the signal before the single track and not acquire the northbound slot.

The slot is released after the train has left the single track section.

At the other end, a train is waiting because the northbound slot is not empty. It does not acquire the southbound slot and proceed past the signal until the northbound slot is empty, indicating that there are no trains using the single line heading north.

This type of layout is useful when terrain, expense or other constraints make double-tracked lines impractical, but more capacity is required than can be achieved by not signalling the single track at all such that only one train could occupy the single track at once.

Other potential uses for slots:

• Complex one train working lines
• Congestion/queueing control
• Deadlock prevention on tricky flat junctions
• Putting trains in loops/sidings to allow trains behind to overtake
• Conditional order dispatch across multiple trains
• Conflict prevention in general
• Prioritisation at junctions

Counters

Counters are named variables which can be modified by a routefinding restriction program when a train passes a signal.
Counters can be used in conditionals in routefinding restrictions and programmable pre-signal programs, and in conditional orders.
The main use case for counters is counting trains and round-robin behaviour.
For counting the number of trains on a particular section of track, slots should be used instead.

Using counters to store state makes "logic trains" and similar workarounds unnecessary.

Counters are not shown in the user interace by default, "Show advanced routing restriction features" must be enabled.

Counters can be created, deleted, renamed and have their value manually changed by selecting "Manage counters" in the train list window "Manage list" dropdown.