Sorry, I know you said "on-highway," but this pic might apply as well...
This Jeep was cobbled together from spare parts, with the express concept of "budget" in mind. Owner didn't think a full rollcage was necessary, as he wouldn't be doing anything "extreme" with it.
FIRST trip out, he was coming down that slope you see in the background of the pic, when the shale gave way and slid the butt end around underneath him. 2.25 flips later, we were scrambling to get his unconscious wife to the hospital. She came out of it with only a headache and a few staples in her head, but we all know things could have been much, much worse.
BTW, his "budget" CJ now has a full rollcage worth probably more than the rest of the Jeep. It isn't the Jeep that's being protected, after all.