dozy drivers

Yesterday afternoon, I drove to Southport. I was most peeved that the dual carriageway was down to one lane and, despite the fact that the speed limit hadn't been reduced, the driver in front of me refused to go over 40, causing something of a tailback. That was annoying enough, but when the speed limit was reduced to 30 - the bugger still kept doing 40!

I suspect that the driver was asleep and the car was on cruise control. What else could explain such piss-poor driving?