I travel back & forth through PF on Route 4 daily and north to Dunkirk or south to Lusby at least once a week, and have never run afoul of the Calvert County Sheriff's department.
I drive the route 4 corridor plenty and have not had that pleasure either, I lock my CC on between 60-65 ish, kind of go with the flow.
Stay in the right lane if I'm not passing. Slow down with traffic in PF.
I'm sure if they were running a speed trap when I went through I would get pulled over, but you don't see too many during rush hour, unless it's the opposing side and it's lightly traveled.
Had a friend, who's wife got a ticket going the opposite way during rush hour. She complained to her husband about the other side of the highway and he just told her they weren't going to try and pick people out of rush hour traffic and cause a traffic jam, you were a much easier target.