This is a tricky issue with cyclists and rules of the road, which I don't have an answer. If a large group rides single file, it's much tougher to pass them vs a group just taking a whole lane and riding as many abreast as can fit in that lane.
I've never seen a law that requires a minimum group of cyclists (there may be a law, but I haven't really looked, since I don't ride in such large groups).
This group had 20-cyclists and if they were in single file, that's more than 120 ft line.
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