Lots of metro systems have lines that function as a hybrid Linear/Loop line, for example a train leaves central station, stops at 4 other stations (A,B,C,D) before heading out into the suburbs in a loop then coming back to Station D and proceeding via C, B, and A to Central again stopping at those four stations in both directions. This would be a good addition to the game.
Like a p-loop? It’s on the Devs to-look-list I think. It was raised a few months ago. Main concern was the massive amount of pathfinding glitches that could appear.