Not OP but limit cars sold in a country to whatever the speed on the freeway is. e.g. in the UK, all cars registered here must have limiters fitted to stop it exceeding 70mph.
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.
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.