I have no idea what speed gets them moving, but I usually drive 70 with the cruise on. In this state I seem to be a small minority. People are either going slower (60 or less) or much faster (80-100). When I drove our RV home I had the cruise set on 55-60 in the lane with the trucks. My back tires are well over the safe age so I wasn't going to push it. I probably still won't push it.