Police often run a speed trap atop a hill along the route. The road's design uses freeway geometries and a wide-open feel. I-95 has a speed limit of 65 mph, but when drivers exit, they find themselves on a road with similar geometry at half the speed limit.
Roads with similar designs can have radically different posted speed limits. You get off one highway posted at 50 or 60 and enter a virtually identical highway posted at half that. What gives?