I believe the PC is hinting about station barriers. Major stations need you to scan a ticket (or con a guard) to get off the platform or out of the station. Min

I believe the PC is hinting about station barriers. Major stations need you to scan a ticket (or con a guard) to get off the platform or out of the station. Minor stations sometimes don't - and if it's your station you'll know. I think the real reason is less sensational: trains that go full in one direction still have to go back in the other direction whether they're full or not.