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Actually, I don't agree with this logic...I know, I know two riders are longer than one but overtaking a car sized object takes longer than overtaking a bike sized object, even if that bike is in a strong primary.
You need to provide another meter or so of clearance to overtake two abreast riders and sometimes, doing that safely takes time.
There is a time and a place for riding two abreast...in my opinion and I know this is an opinion that is not shared by many.
Riding two abreast is a great experience but one soon spoiled by angry drivers, why not just filter back and wave through drivers, get a toot of thanks and then ride back in formation.
Result, everyone has a great day, a great experience and no one takes to the Internet in fury.
As,for the milk float tractor analogy, on a good sunny day I see literally hundreds of cyclists enjoying the road...I think I've seen three tractors in my riding life and never...ever...encountered a milk float.
Horses, now I see tons of them, that would have been a better comparison. For some reason drivers give horses massive respect.
Cyclists are not as nice as horses, clearly.
Edit, overtaking a peloton is a different thing and I totally agree that bunching and riding two or even three abreast is often safer for all parties.
But just two riders?...chill and communicate.