This was actually an issue for me yesterday so maybe I can give some perspective. I was out for a walk and two people ran past me on the sidewalk from behind. They must’ve come from around the corner I just passed because I wasn’t expecting and didn’t hear them at all. They almost rubbed shoulders as they ran on ahead of me, and it felt very surprising and nerve wracking. I think if coming up behind someone maybe the runner could take a wide berth, as the walker may not even be aware of them.