fontana wrote:I would have thought two a breast would be more dangerous from the point of view of vehicles overtaking.
Surely it's safer to give vehicles as much space as possible to get passed, especially on country roads.
That would seem to be logical, but on a lot of roads, it is much safer to be two abreast or in a dominant position. On many of the roads I cycle on (B roads), there is barely room for two cars and a cyclist side-by-side. But if I am towards the left with a car about to pass in the opposite direction and a car coming up behind, a significant number of drivers (one on most rides) will push through the gap. That leaves me, the squidgy soft one, with no escape room. I can assure you that can be very scary, especially if as happened a couple of times, the overtaking vehicle is an artic.
So, by riding two abreast, you force the overtaking driver to wait behind until the car coming the other way has passed. And the driver will go further over to pass, thus leaving the riders some option.
Also, in a group, the length of the group is halved if they are riding two abreast. That reduces the risk of a driver starting to pass a single file group, and having to squeeze the lead rider(s) into the ditch to avoid a vehicle coming the other way.
Pete, out of respect (you've done the job and I haven't), I withdraw my earlier speculation about what led up to the two cyclists being stopped.