.......... One possibility there is for the chairman to have a limited power to force-park a member's trains. Might be it could only be used once in 24 hours, or something.
This I absolutely agree with. A recent event in my team brought this home to me very strongly. There needs to be a facility to allow a chair or deputy to stop the engines of a player who does not return. If a good players, there will be a very good reason indeed why they have suddenly dropped from the game.