Do NOT get me started! 
Slower speeds and speed cameras play a big part in this, they set the cruise control @ 65 mph and think they have every right to be in any lane, then doze off staring straight ahead oblivious to faster moving traffic.
The most dangerous ones are listening to the sat nav, they hear " keep right at next junction" the cue to get as far right as possible without thought or logic.
Loads do not drive, they sit there holding a steering wheel waiting for the next instruction while dozing in a comfortable seat causing frustration to others.