I observed speed limit enforcement for the first time in a very long time on the George Washington Memorial Parkway on the northbound side, just north of the Arlington Memorial Bridge on Columbia Island in D.C.
A U.S. Park Police motorcycle officer was using a hand-held radar set to check traffic just north of the Memorial Bridge. Never seen any speed enforcement at that particular location (and never any speed limit enforcement on the Parkway on Columbia Island ever).
Posted speed limit there is 40 MPH (though the 85th percentile speed is probably north of 60 MPH).