What's the difference? If someone's on the track and gets hit by either type of train they're going to get seriously injured, or even killed.The clue is in the name:
Docklands LIGHT Railway.
Light Trains the regs don't require them for driverless trains.
Heavy trains do.
Again, how come they are not on the surface stations of the JL?
I would go and put this over to the bods at RailUK, if it wasn't for the fact that a) it might not show up for two days, and b) it's the middle of the night.