I've seen this happen in the Sunday morning Como Street ride out here in SoCal... the speeds are pretty much in the low to mid 20's and faster for most of the ride/race.... probably about 50 riders or so.. and they will take up the bike lane and most of the right lane... it is a 2 lane road each way, and traffic can go around... I thought it was kinda odd as well, but went along with it... it isn't a super busy road at 8:30 on a Sunday Morning

Jeff