BC9000
The BC9000 is a sign to manage anticollision system in intersection.
It must be associated with any BC90XX sign (except BC9001), including another BC9000 sign.
This sign is placed upstream from the intersection, on 1 branch, and is associated with another BC90XX upstream from the intersection on the other branch. Each sign has an escape track : for BC90XX it will usually be to turn left, for BC9000 turn right. The whole construction must form a 3x3 square. On the picture below, BC9000 sign is under the clear wood block, while BC90XX sign is under the dark wood block.
What BC9000 does is to synchronize its own lever with the lever of the associated BC90XX, giving 2 possible positions : OFF-OFF or ON-ON. Moreover the position can switch only if there is no risk to break a train.
Giving this rule, the preferred strategy of BC9000 is to power the 2 levers when a cart passes on it, meaning to switch to ON-ON position whenever possible, providing that no train will be broken during operation.
On the other side, the preferred strategy of BC90XX is to satisfy routing layer, switching to the correct position (OFF-OFF or ON-ON) if necessary, providing that no train will be broken during operation.
On both sides, if preferred strategy can't be satisfied in order to avoid collision, one of the track will be deviated to alternate path. In other words, anticollision layer has priority over routing layer.
BC9000 sign must be placed under a rail. At least a lever should be present on the left or on the right of the sign to command an intersection that can make the cart go straight or turn in escape track. the collision point must be 3 blocks behind the sign. It must be associated with another BC00XX sign placed so that the collision point is also 3 blocks behind it.
Line #1 : Free
Line #2 : [BC9000]
Line #3 : Free
Line #4 : Free