Sharp Park Road, Paifica, CA?
I looked at it on Google Maps and (at least eastbound first portion) the shoulder looks like my daily commute, except I have very flat and mostly straight. I'm doing 15-18 mph on 40 mph posted (so they're doing 50-60 mph).
I have some points where the shoulder pinches out, and at those locations I take the center of the right hand lane. I have a mirror which I'm monitoring constantly. If there is a pack of motor vehicles that will arrive when I need to take the lane, I'll pull over and let them by. My experience is that packs of vehicles are potentially dangerous.