pasty
A different kind of pasty
I still don't really get the doors thing. What's the safety issue, that the doors close on someone? That someone falls down into the gap? Can that even happen?
As I see it, as a passenger, it is because a guard is stationed somewhere in the middle (ish) of a train, and can also get off and stand on the platform, look up and down to make sure it is safe and clear to shut the doors and move off. A driver on his own cannot possibly do that.