Trap Road exits off the parallel toll road to Wolf Trap Farm Park. As you are heading to Dulles Airport on the Dulles Access Road, just after you pass under Trap road the barrier on your right is in two parts: a metal guard rail and a concrete barrier. This splits with a drain at the western (nearest the airport) end of the guard rail. The drain is sunk so low, you cannot see the patrol car until after you have passed and can look back. Of course, by then it is too late. I take a bus along the road and frequently see the patrol car in there from my high seat in the bus.