When i first cycled in France, in the early 80s, it was almost universal to toot the horn when a car was approaching from behind.
Cars would slow, toot and then overtake, of course, even in France, these days have long gone, now its zoom past at high speed and the only warning is the roar of tires and the rush of the air as the vehicle comes past... narrowly missing the on coming car from the other direction......
Just back from France, even in very rural areas we were in, i had the impression they were trying to kill me, worse than here in the UK, so little wonder i hardly saw any local cyclists about and France still has no TdF winners.
I think the its an excellent idea, it would (perhaps) make drivers consider what they are doing and not blindly speed past and which sport does INEOS sponsor?
On the 1.5m thingy, i'd rather vehicles slowed down, cars regularly come past me at 2m plus but at 60mph, it doesn't feel like 2m...