Did you never see Bonekickers?
LLB - I think sheddy probably (I may be wrong), means people get into cars and rely on the heated windscreens to clear the snow or ice, meaning they probably drive off with the merest letterbox area cleared to peer through, and the first time they stop, the snow on the roof slides down and obscures the screen all over again....
I cleared my Mum's car yesterday morning, with a broom, barely a flake left clinging to it by the time I finished - screens, roof, side windows, mirrors, lights, plates. But a lot of people Idiots don't bother.
I've always taken Moton to mean that sort of driver that none of us would want to admit to being - thoughtless, in a world of their own, impatient. Not all motorists are motons, but if someone doesn't clear their car properly, they probably are...