At the north end of N Glebe Rd just before Chain Bridge
Arlington police frequently stake out this location as the short amount of distance given to drivers to decelerate from 35mph to 25mph almost guarantees a steady stream of revenue. They will often park their car on the west side of the road, out of sight around a curve and then stand in the large median between the north and south-bound lanes of N Glebe Rd (38°55’32.7″N 77°07’29.1″W) just before the road goes downhill to Chain Bridge. This gives them a clear line of sight up Glebe and good concealment in front of the trees in the median. Their mandatory safety vest gives them away though and if you have good eyesight, you can spot them from a distance. If you see them before passing N River St then you could probably turn left onto N River to avoid them (I do not advocate any illegal activity, but they are unlikely to abandon their post, and you would be well on your way by the time they could get to their car, turn around, and come looking for you in the maze of residential streets that N River leads into). After N River, you are trapped. You can easily bypass the entire area using a combination of Old Dominion and Kirby Road on the west side of N Glebe or 26th/31st Streets and Military Road to the east of N Glebe.