Rail chain signal

Rail chain signal

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Recipe
0.5 + 1 + 5 → 1
Total raw
1.75 + 1.5 + 6
Map color
Health	100 130 160 190 250
Stack size	50
Rocket capacity	50 (1 stack)
Mining time	0.1
Prototype type	rail-chain-signal
Internal name	rail-chain-signal
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Rail chain signals are used for automated transportation on a railway network. With rail chain signals, it is possible to use multiple trains on a single track, or multiple rails that intertwine.

Basic

• The best prerequisite to understand chain signals is to understand signal blocks.
• Rail chain signals are placed like block signals at the right side of a segment.
• They work similar to pre-signals in OpenTTD.

Definition

While normal signal prevents train from entering the occupied block, chain signal prevents train from entering a block if it won't be able to leave. When more than one exits exist, the one where the train is pathing to is considered.

Usage examples

Regular signal compared to a chain signal

With a regular signal, the block after it is empty, so the train can go there.

Chain signal with one exit doesn't allow the train to enter the block, since it can't leave immediately.

Simple example with practical usage

The chain signal prevents the train from blocking the crossing route while waiting.

Double crossing

Double crossings are a common cause of train jams, as trains can stop in the middle of the crossing and block everything. It can even cause total deadlock, which require manual intervention to fix the problem. With chain signals, the rails that don't cross are still separated, but trains won't stop in the middle of the crossing.

Deadlock prevention

Another common cause of blockages are bidirectional single track lines with occasional bypasses. Here a train can't enter the line because another train is in it, but that train in turn can't leave the line.

With chain signals, this problem can be totally avoided by preventing the train from going to the shared section unless it can exit it.

Advanced

Some good pictures are at the Friday Facts #81 page.

• If the chain signal has only one exit, it doesn't allow the train to enter its block, if the train would have to stop in said block.
• Since trains react to chain signals based on their own path, chain signals before a crossing will not stop trains if the other track's exit is blocked.
• If there are several chain signals before a regular one, a train waits before the first chain signal if the block after the regular signal is occupied.

• If a chain signal switches to green, all exits are free.
• If it switches to yellow, the block is reserved for a train and all entrance signals of that block turn red.
• If it switches to red, all exits are occupied.
• If it switches to blue, some but not all exits are free.

History

• 0.16.0:
  • Rail chain signals can be read by the circuit network.

• 0.12.0:
  • Introduced

See also

• Rail signal
• Railway
• Tutorial: Train signals