Not wishing to be the sceptic here Roger, but it's more like 80%. Even seasoned drivers like myself have bad habbits.
It is more likely that a fresh from driving school driver will be more wary, well at least until the first "Boy racer/Laddette" belts past with the obligatory drain pipe poking out of the bucket sized cut out of a 1.2 Ltr Corsa.
There's no reason at all why even a 17 year old can't tow a trailer, I did back in 1977.
Today though in todays traffic, I would freely welcome driver assessments say for those 40 and over, and these should take place every 5 years in my oppinion. Perhaps a simple half hour assessment and de-brief would keep everyone at the "top of their game".
I've been assessed by 5 different car manufacturers/motoring safety bodies in the last 10 years, which I found both enlightening and beneficial. Quite easy now to spot the growling grannies in the shade on a sunny day and the budding clarksons on the A19.
Joking appart, continual assessment and also making the motorway part of a driving test would start to bring a standard of driving back to the uk.
I'd better whip the flack jacket on now!
Steve L.