When it is desirable that trains only ever go in one direction over a piece of track, an always-powered blocker sign can be used. This is useful when having two tracks side-by-side, each going in opposing directions. The path finding system will automatically ignore paths that are blocked by blocker signs.
With [+train:left] trains coming from the left are blocked, only allowing movement from right to left. Similarly, [+train:right] and other directions can be used.
