Actually, it’s only a small section of the M1 – near Sheffield – but the media likes to distort these things.
I wrote about this subject a few years ago. That was at a time where they had only recently been talking about raising the speed limit! My main point was that although cars emit less pollution when driven at 60mph instead of 70mph, they they take longer to pass through a given area at 60mph, so the reduction in pollution is pretty much negligible. It’s a case of comparing a quick but pungent fart with a longer, less smelly one.
The other thing I think I mentioned is the stench when you drive on the M1 past Sheffield and the wind is in the right direction. And it doesn’t come from cars – it’s from the factories around there, and a smell like that isn’t going to contain anything that is good for you.
An even greater irony this time around is that London is currently in the grip of an extremely poor period of air quality. They haven’t quite got round to blaming it on cars and lorries yet – that’s been done before – but at the moment the most direct blame has been placed at the feet of pretentious people burning wood during the cold weather (though that detail seems to have been removed from some reports).