I'm sure one of y'all knows what this really is, but that's not nearly as much fun as Jade Helming it
It looks like one of the wheeled devices linemen pull along the lines to knock ice off unheated lines, so they don't sag and snap under the weight of it.
I've also seen something similar, used to run fiber-optic cable along pre-existing lines.
May not be either of those, as I don't see any extra attachment.