[jiggy2011]

The radio , passengers and thoughts are much more passive and easy to tune out but even then I'm sure there have been plenty of accidents that are caused by daydreaming. A passenger can see out of the window and has awareness of the car's surroundings so they will usually know to shut up or at least not expect a quick answer to their question if you are doing a tricky manoeuvre. Electronic devices or people on the other end of a hands-free conversation both require interaction and do not have awareness of the situation that the driver is in.