The blocker sign allows you to block trains coming from a certain direction. It is also used during path finding to block certain routes from being used. For example, if your trains are getting sent into the wrong direction, possibly colliding with other trains, you can use the blocker sign to prevent this.
The sign needs to be powered for it to function. It does not have to be powered for it to be used during path finding. It operates on both flat and ramped rails, so it allows you to stop a train while it slides down a ramp. Players cannot push the train past the blocker sign, but they can push it the other way since that direction is not blocked.
Therefore, blocker signs do not indefinitely freeze the train until power is removed, you can still push it in the other direction.
After train or cart, you can specify the direction to block. (just like you can with every other sign)
You can use the types defined below. If left empty ([train]), the train has to face the text-side of the sign to be blocked. The type is defined by the first letter, so instead of right you can also use r on the line.
For use with path finding, always use the always-powered [+train] syntax on blocker signs, otherwise it does not work.
|north||Trains coming from the north are blocked|
|south||Trains coming from the south are blocked|
|east||Trains coming from the east are blocked|
|west||Trains coming from the west are blocked|
|left||Trains coming from the left (relative to the sign) are blocked|
|right||Trains coming from the right (relative to the sign) are blocked|
|backwards||Trains coming from the back (relative to the sign) are blocked|
|forwards||Same result as if you keep the line empty|
Third and Fourth line
Similar to the station sign, you can add an optional action to perform after the blocker sign loses power. Options are left, right, continue and reverse. If left empty, the train is not moved at all. All actions launch with the same velocity as the train had when entering the blocker sign, no actual launching is performed. The third line is used for a delay, the fourth specifies the direction to launch to.
https://www.youtube.com/watch?v=S1ERZDwJnZk Important: Syntax has changed over time. Use [train:left] to block trains coming from the left. The third line no longer defines the direction!