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. <gallery mode="slideshow"> File:Pathfinding_Blocker.png|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. </gallery>
当希望某条轨道上只能单向行驶时，可以使用始终开启的阻挡器，这个方法在有并排的轨道上时很有用，每条轨道只能沿着一个方向行驶，路线查找会自动忽略被阻挡器阻挡的路线，使之不会出现驶错轨道的问题。
使用 [+train:left] 只会允许从右向左行驶的列车。同样，你也可以使用 [+train:right] 阻挡从右驶来的列车。
