I'm no train expert but I would say that anything that involves being at the helm of a heavy moving object requires attention. Sure there will be times where it is plain sailing but it doesn't send out the right message when they are caught in the act of not focusing on the job.
The driver needs to be in a position to react to information that he receives from those running the lines.
Every time I visit New York I see drivers reading newspapers etc. on the trains. Their job is pretty simple and 95% of the time very mundane. I would prefer they pay attention when my life is in their hands, but this isn't an unusual thing.
Yeah, I mean clearly there is the 5% of the time where their human skill is required on those trains, but it's how do they react to information that they may receive regarding troubles on the line ahead.
I suppose reading a newspaper is far safer than say listening to music, where their hearing is limited.