The danger is coming up behind a lorry - that you can't see in front of, so can't see the traffic braking far ahead, so the lorry might slam on it's air brakes out of the blue - while having to keep an almost constant eye on the mirror, trying to judge the speed of vehicles in the adjacent lane, when frequently it is so busy it takes a long time for enough of a gap to appear to pull out into, so you're looking in the mirror an unhealthily-long time. Meanwhile you're slowing - like for instance some arctic up ahead is going uphill - while the cars in the next lane are going as fast as ever, so you're looking at pulling out and stamping on the gas to get up to speed before the car behind is spooked, if not actually rear-ending you. You have to simultaneously look intently in the mirror, trying to judge the speed and distance of the vehicle you think you might be able to pull out in front of, weighing that up, and watching the proximity of the lorry in front you're closing on - why, after all, you want to overtake - ready to react in a split second if its brake lights come on, and preparing yourself to accelerate hard when you do pull out.
You might say that, in that situation the responsible thing to do is stay behind the lorry; but that still involves the driving while almost constantly looking in the mirror, behind the lorry you can't see in front of, that might drop it's superior anchor at any moment (or be gradually decelerating - and into whose slipstream you might enter causing you to accelerate without consciously choosing to).
To which you might say, and might as well say, to just stay behind the lorry and don't even consider changing lanes. After all, if you maintain a safe braking distance, you'll get a partial view of the traffic up ahead. Of course, someone always pulls into the gap you left - in the leftmost lane, usually for taking the upcoming exit, or because the driver, anxious to appear law-abiding, keeps overtaking then returning to that lane, so that instead of an almost straight line, they drive the motorways zig-zagging the entire length, not only multiplying their own opportunities to make a mistake, but adding another potential distraction for everyone else on the road..
Driving in the slow lane, behind the arctics, is about as safe as driving on the hard shoulder: that is, theoretically. Or, perhaps, hypothetically, given that it requires driving behaviour so rarely seen as to be the exception. It isn't that motorway driving is high risk if you don't follow the Highway Code to the letter; but because 'people'. Mostly, imho, people who don't do their utmost to see what's happening in the distance rather than just what the vehicle immediately in front is doing - while not having safe braking distance, i.e. having insufficient awareness, doing insufficient forward planning. And the worst lane for that is the one with the arctics in.
The answer is not 'follow the Highway Code', a suggestion that in the absense of evidence of compliance looks like petulance. The answer - short of electric vehicles remotely controlled by some track beneath the road - is making the test an advanced driving course. Which I can't see ever happening.
I tend to avoid the motorways.
Biting the hand that feeds IT
