GW Parkway is U.S. Park Police area of patrol. Posted speed limit is 40mph however safe/common travel speed is around 60 mph. The enforcement officer will typically either stay in a parked patrol car on the overpass coming from Nation Airport to south bound G.W. Parkway -or- park directly in front of Maintenance Yard pointing at south bound traffic. Primarily have seen laser in use during the past year. The officer will sit in the vehicle and the laser reading is typically taken immediately after you reach crest of small rise on South bound travel lanes. Watch the cabs going to National Airport. They have radio and cell phones and typically let each other know when the trap is set so if you see them poking along at 35, be careful!