Traffic oddities 1: Clumps.

So I’m cruising along at somewhere around 5 mph under the speed limit and getting ready to switch lanes and pass another truck when up from the rear comes another clump.  Clump of what you ask?  Dirt?  Grass?  Hair?  Not quite, a clump of cars actually.  The clump I refer to means a group of driver going around the same speed and slowly single line passing all the other cars, I call it a clump because it will often take up both lanes till it hits a slower vehicle.  This is a weird and annoying phenomenon, I can cruise for fifteen minutes without seeing another car in my direction on say the I-84 then bam!  Fifteen cars come up from behind, and go, then there is nothing for a while.  I think its a subconscious phenomenon amongst drivers, they do not like being alone so they clump up with others going similar speeds.  Maybe, I could be off my rocker here but I have seen this thing happen on every major interstate I have driven.  NO MOAR CLUMPS!!!