This would prevent speeding (but stop overtaking) on motorways, which I argue are the roads that need the least speed control. Speeding is probably more harmful on all other roads where you have pedestrians, cyclists and complex road layouts.

I agree, but if the goal is to simply stop speeding, it will stop it on motorways. Whether it has any safety benefits or not is incidental.

Well there's the problem. Why is that a goal. http://www.sehinc.com/news/truth-about-speed-limits-explaine...

Oh sorry - to be clear, I was being a little pedantic about he question the parent mentioned - what is his solution to stopping speeding. I agree that reducing Speed limits (particularly on motorways) isn’t the answer. There are other reasons for it however, eg Ireland [0] is attempting to reduce the speed for environmental reasons.

[0] https://www.google.co.uk/amp/s/www.irishtimes.com/news/irela...

This will result in lives lost when people can’t overtake.

I don't see how this could happen. What scenario could you be in that you can safely overtake (at 70+mph) that you can't avoid by slowing down?

Sure, but it will save many more lives by reducing speeding.