I think all the clubs here reckon two abreast as the safest way to move, as the cars have to treat the group like another car and not like some annoying narrow obstruction they could probably squeeze by.
But when there's a lot of traffic we split up into groups of max ten or so, i.e. 5 pairs, which isn't hard for a car to pass if the opposite lane is clear.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett