The biggest danger I see today is people using mobile phones even though its a "points" offence, however its only "points"  

 

For a good example of that, see about half way through this video: https://youtu.be/eaHKjjsocm0?t=327

 

Those kids are so engrossed in their phone, lunch, lipstick, lord knows what that they don't even notice bends in the road, let alone other road users that might have been there - one drives straight off the side and looks so non-plussed it's like she must do that every day!  Scary..

Why does "passing either side" work in N. America?

FWIW, it's only allowed on 3+ lane divided highways, often where all the lanes are moving at or close to the posted speed limits (including the big rigs).

DC

This is true. If you tried to apply the undertaking rule on a 10+ lane wide highway (either side) it just wouldn't work.

The most lanes I've seen in the UK on one side of the motorway is 6. Two of those lanes were added to accommodate an upcoming motorway split so traffic could keep flowing smoothly onto the next carriageway /motorway.

Most of the time when it was 6 lanes, it was seperated with thicker lines to indicate an upcoming road split.

I maybe wrong and there probably are wider sections of road in the UK, but when even the trucks are allowed to do the speed limit (as they are in N America), there is little way the undertaking rule could work.

It is essentially a free for all and so you do have to have your wits about you at all times, otherwise you will miss that low slung sports car sliding up your inside when you're crusin along in your jacked up 8.2ltr V8 Hemi pickup!