Photo radar from unmarked civilan version Ford Crown Victorias (not police package vehicles – they lack police radio antennas and some of them have aluminum mag wheels). The vehicles have a box-shaped radar antenna on the front bumper, next to a single Hella driving/fog lamp that has been retrofitted with a flash bulb inside. Vehicles traveling more than 11 MPH above the posted limit are photographed. See http://mpdc.dc.gov/info/traffic/ speedlocation_map.shtm for a listing of potential locations. These units seem to snap photos approximately once every 20 seconds on a moderately traveled street.