Reverse loop
Are we talking about isolating a section of track?
You need a block at a reverse loop or you short out the track.
You can set up a block at a crossover to stop one train while another passes through. Or set up a block on a loop so two trains will run together but not collide. Ablock is a ection of track that the current can be reversed or it can be shut for a delayed time while a track section ahead is clearing.
Bob