I'm not a railway person admittedly but I have travelled on an awful lot of them. What I've noticed is this. At most stations there is someone on the platform holding a white table tennis bat that allows the guard and driver to see that the doors can be closed / train can leave. Admittedly not...
Left my house in Portslade at ten to six. Got to my seat two minutes before kick off without any beer. The friend who came with us had to leave work and get her babysitter in early then couldn't get on an Eastbound train at Shoreham because it was too busy. Everything Coastway West was late...