Train Signals

Block Signal
Train Signals are used to direct the movement of Trains to avoid collisions and bottlenecks. Block Signals can be placed on Railways to create 'Blocks' between each other. When a Train is occupying such a Block, other Trains will be unable to enter it. Caution: Signals are directional! Trains are unable to move against this direction, so be sure to set up Signals in both directions for bi-directional Railways.
Unlocked by	Tier 6 - Monorail Train Technology
Class name	Desc_RailroadBlockSignal_C
Ingre­dients
2 ×  Steel Pipe
1 ×  Copper Sheet
2 ×  Circuit Board

Path Signal
Train Signals are used to direct the movement of Trains to avoid collisions and bottlenecks. Path Signals are advanced signals that are especially useful for bi-directional Railways and complex intersections. They function similarly to Block Signals but rather than occupying the entire Block, Trains can reserve a specific path through it and will only enter the Block if their path allows them to fully pass through it. Caution: Signals are directional! Trains are unable to move against this direction, so be sure to set up Signals in both directions for bi-directional Railways.
Unlocked by	Tier 6 - Monorail Train Technology
Class name	Desc_RailroadPathSignal_C
Ingre­dients
2 ×  Steel Pipe
1 ×  Copper Sheet
1 ×  Computer

Block Signals and Path Signals are structures that attach to Railways, used to control the flow of trains. They are necessary if you wish to have more than two trains using the same railway without collisions.

Construction

Both types of train signals can only be built on the joints of constructed Railway tracks and will automatically snap to them.

The forward direction of the signal is determined by which side of the joint is targeted. It helps to point at the track rather than the edge of the track. An arrow also indicates the forward direction.

Up to 2 signals facing opposite directions can be placed on each track joint. If only one signal is present, it will prevent trains in the opposite direction from passing through. A bi-directional track can be achieved by placing signals on both sides of the track.

Train Signals can be set up for right-hand traffic (common) by placing on the right in direction of travel, or left-hand drive (less common) by placing on the left in direction of travel.

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  Block Signal placement

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  Double Signal (Path and Block) placement

Usage

Pathfinding

Automated trains will stop at a red or error signal. They will also brake ahead, although they will be forcefully stopped if they fail to slow down on their own.

An important aspect of train pathfinding is that it does not re-route. A path is determined by the shortest distance to the destination, regardless of whether it is occupied by other trains. Trains won't pass the back of a signal, so an incorrect setup can make the destination unreachable.

Train Stations the train is passing through add a +100m distance penalty. Rail stackers cannot be constructed, instead, long snake tracks have to be used as waiting areas.

Signals can be completely ignored while driving trains manually. Block Signals will recognize that they are occupied like usual. However, Path Signals will prevent all trains from entering if their block is occupied by a manually-driven train.

Blocks

A block is the area between two signals. A block which contains any part of a train is considered to be occupied, otherwise it is vacant.

Blocks are colored while a signal is being placed. Each block is given a different color and colors can be repeated on "other blocks". It can help understand signal placement errors to select a signal to place then examine where each block begins and ends by looking at their coloring.

Blocks have to have at least one entry signal, as well as at least one exit signal (which will be the next block's entry signal). Blocks on a linear track will have only one entry and one exit signal, but branches will have multiple exit signals, merges will have multiple entry signals, and more complex intersections can have multiple entry and multiple exit signals. All entry signals for a block have to be of the same type, either all Block Signals or all Path Signals.

Rails which touch or clip through other rails will be considered part of the same block, even if the rails do not snap together at the ends: this makes it possible to build crossroads where one track crosses another. This can lead to many issues with signalling if two tracks in opposite directions are built too close to each other, and unknowingly "intersect" at curves, for example.

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  Block examples

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  Block colors shown when a Signal is being placed

Block Signal

Block Signals work on a simple principle: they prevent a train entering a block if another train occupies it. If any part of a train is a block ahead then all Block Signals entering that block will be red, preventing entry into that block by other trains. If the block ahead is empty, then all Block Signals entering that block will be green.

Block Signals are typically used on straight double tracks and for stations. Bidirectional tracks and junctions are better handled by Path Signals.

Note: Block Signals shouldn't be used for blocks where tracks merge from mutliple entrances. Due to a bug (see below), multiple trains might be able to enter and collide, even if the junction is signalled properly.

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  Example of placing Block Signals for Train Stations

Path Signal

Path Signals are more advanced than Block Signals. They use a path reservation system to control trains. While avoidable in many scenarios, Path Signals make managing advanced networks possible.

The three important aspects of Path Signals are that they allow multiple trains to enter if their paths within the block do not intersect, do not allow a train to enter if it cannot exit, and that a Train Station cannot be within a path block.

Using Path Signals for junctions is not strictly necessary in most cases. However, it is recommended if you are building high-traffic systems with high chances of multiple trains reaching the same intersection. In this specific context, you will often hear players use the phrase "path in, block out." This is because all entry signals of a block must be of the same type. You cannot have a Block Signal and a Path Signal leading into the same junction.

Due to a bug (see § Current issues), path blocks have to be level, or trains may collide into each other.

Advanced description

Path Signals automatically subdivide a block into paths, and treat them as individual sub-blocks. An automated train will reserve a path through the block as it approaches. Other trains can reserve their own paths at the same time, as long as they do not intersect with a path that is already reserved by another train. This allows multiple trains to pass through the same block simultaneously without colliding.

Unlike Block Signals, Path Signals will "look ahead" to the Block Signal that follows a train's reserved path. The Path Signal will stop a train if it would have to stop for the next Block Signal while still traversing its reserved path. The Path Signal will turn green once the block at the end of the reserved path is vacant. This system ensures that trains do not stop in the middle of an intersection, which helps to prevent gridlocks. However, trains can be forced to stop within an intersection if their desired exit block becomes occupied with a manually driven train.

Path Signals remain red until an automated train has reserved a path through that signal, at which time they will turn green to allow the train through. Automated trains treat the Path Signal as red until it turns green because it has approved the path. An approaching automated train will not reserve a path through a Path Signal's block until the next signal is the Path Signal. This means that if there is a Block Signal just before the Path Signal, the Automated train will have to slow down because the Path Signal will remain red until the train passes the Block Signal.

It is possible to chain Path Signals one after the other for especially complex intersections to increase their throughput. Trains reserve paths through multiple Path Signals at once up to the next Block Signal, and will not pass the first Path Signal if any single portion of the path cannot be reserved.

There is no way for a player who is manually driving a train to reserve a path through a Path Signal, so a player will always appear to be "running a red" when they pass through a Path Signal, even though the block ahead is vacant. When a player-driven train enters a Path Signal, the entire block seems to be considered occupied, and the Path Signals will act like Block Signals and not allow automated trains to enter.

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  Example Path Signal block

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  Example Path Signal block usage

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  Double track "T" intersection using signals

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  Single track "+" intersection using signals

States

Individual Train Signals can appear in one of three "states" that reflect if Train is ok to proceed, or must stop, or there is an issue/error with Train Signal placement. Error signals are treated as red.

• 🟢 Green
  • Block Clear (Block Signal default state)
  • Path Approved (Path Signal)
• 🔴 Red
  • Block Occupied
  • Waiting for Path Reservation (Path Signal default state)
• ⚠️ Error
  • Invalid Signal
  • Signal has missing connections
    • The signal is placed on the very end of a Railway or is not connected to one, leading nowhere
  • Block has no exit signal
  • Block has conflicting entry signal types
    • All entry signals have to be either Block or Path, this does not apply to exit signals
  • Path block cannot contain stations
  • Signal loops into itself
    • This error means the signal failed to divide a block, even when no loops are present. It can occur when, for example, two unconnected tracks are too close to each other and a signal is placed on one of them.
    • Sometimes, there is no obvious cause for this error. Using the block color highlight can be used to diagnose which signal is causing the problem. Rebuilding the affected junction can resolve the issue.

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  Train Signal error

• 

  Train Signal error UI

Tips

• Track joints can be found easily by aiming at a Railway in dismantle mode.
• Collisions generally shouldn't happen if any signals are in place. Gridlocks may occur instead. See § Current issues for exceptions.
• Trains appear to slow down for red/error signals at a distance of about 250 m, or 2.5 maximum track lengths. If they fail to brake in time (if the block has a steep downhill slope, for example), they will be forcefully stopped at the signal, much like with Train Stations.
  • Path Signals are red until reserved, and they aren't reserved until the train is in a block immediately before the Path Signal. Thus, blocks leading to Path Signals should be long enough to prevent trains slowing down due to approaching a red signal.
• There isn't a general guidance for appropriate block sizes. A good factor is the length of the longest trains. To avoid signal spam, blocks even 3 or 4 maximum track lengths long (300-400 m) are appropriate.

Trivia

• Train signals were originally planned for Update 6.

Current issues

• Train collisions can occur even with seemingly properly placed signals:
  • A train can be made to loop into itself within one block (much like in Snake).
  • More than one entry Block Signal may turn green once a block is freed. This allows multiple trains awaiting entry to enter simultaneously. If their paths cross within the block, they will collide.
    • This can be mitigated by using Path Signals for blocks where tracks merge, which don't seem to suffer from this issue.
• Trains may ignore signals the first few moments after a save file is loaded, causing them to pass a red signal
• Path Signals do not properly subdivide blocks if the Railways are not level, and thus may allow trains whose paths intersect to enter

External links

• Train Signal Guide by TotalXclipse on YouTube
• Signal Logic Rules by u/Sevrahn on Reddit

History

• Patch 0.8.2.4: Fixed Railway Block/Path Signal Visualization crashing for Multiplayer / Dedicated Servers Clients
• Patch 0.8.2.0: Fixed railroad track signal visualization.
• Patch 0.5.2.1
  • Train Stations cannot be placed inside Path blocks anymore, Path Signals now give a proper error message if a Train Station is found inside a block
  • Short blocks, about 75% the size of a Freight Car, should now work with Path Signals
  • Fixed Path Signals placed right after a Train Station being incorrectly reserved by trains going to the Train Station.
• Patch 0.5.1.13: Multiple fixes related to issues with Path Signals and Block Signals
• Patch 0.5.1.11: Potential fix for multiblock reservation issues for Train Signals
• Patch 0.5.1.4
  • Fixed a bug where trains docked at a Train Station could reserve Path Signals when saving and loading
  • Fixed a case where trains approaching Train Stations with a Path Signal right after the station would reserve the same Path Signal over and over
• Patch 0.5.0.11: Added Block/Path Signal visual feedback when placing down
• Patch 0.5.0.0: Introduced