THAT's what those were!
Came across the article " Minnesota Aims to be Model for Wind Transport " and when I saw the photo of the nacelle (don't ask me how to pronounce that) on the flatbed semi I realized, "That's what we saw coming down the freeway!"  On at least two separate trips, Ruth and I spotted these coming  the opposite direction, and had no idea what they are.  They look like a missile cone, except that no missile would have things jutting off the side of it...