The rule would manifest itself in some sort of control in the train design/assembly systems, which would forbid a combination of wagons totalling 256 axles. Tha

The rule would manifest itself in some sort of control in the train design/assembly systems, which would forbid a combination of wagons totalling 256 axles. That way, the issue would never reach the shunters who actually assemble the train, as the list they receive would always avoid that situation.