As always, what's the root problem? Manners. Nobody has any manners anymore and therefore refuse to let anybody get past them, don't care about tailgating or cutting in, don't think they need to bother with indicating. IMHO if we all had a few more manners, we'd have half the problems we have on the roads
Well I said I was going to keep out of this, but I couldn't let your hitting the nail on the head go without comment.
The biggest problem on our roads is lack of courtesy - people thinking their time and their journey is more important than everyone else's. Worse still, I think many drivers see themselves as the only person on the road - all of the other vehicles are just obstacles to get around,. Those vehicles contain other drivers - live, sentient beings who are also trying to get from A to B and who have no time for people who deliberately make that task more difficult, dangerous or time consuming.
Selfish behaviour comes in many forms. It's tailgating the car in front in the outside lane, even though it's either keeping up with traffic or actually overtaking a car in the lane to the left. Equally, it's sticking to what you believe to be the limit in roadworks, while making sure that you've got a good half mile of clear tarmac ahead of you so you can go as fast as you like once you've passed the last SPECS camera.
I'll gladly accept Heckler's 20% rule though - that seems fair enough. That's 40 in a 50 in real terms (though a fraction over 40 on the needle in most cars.) 30 in a 40 (without good reason) will always bug me though, and don't get me started on the numpties that do 30-40mph along the A5117 because they recognise a speed camera warning sign when they see one, but don't realise what the white circle with the black diagonal line is all about.