I seriously can't see how anyone can say a sign telling people not to lean out of the window when the train is moving is inadequate. What can that possibly mean? Errr.... don't lean out of the window when the train is moving? Oh yes. That must be it.
//The presence of trees which hadn’t been inspected / cut back for 10 years and an inadequate sign falls far short of those responsibilities.//
The chap on the Gatwick Express struck a bridge parapet, Zacs. The object struck is not really the issue. As I think you mentioned earlier, there are all sorts of hazards lineside over which the train operators have no control.