I think the "stay back" hand is the crucial extra detail here. It indicates that you are not just in the middle of the highway for no reason, and that you are aware of their presence, and working toward the "common good". It indicates that maybe you know something about the circumstances that they don't, like a car approaching around the bend.

Of course, I know the task is harder for a lot of people in more rural areas who have "thin, fast, busy" roads and much fewer route options...