A radar speed sign is efficient against all kinds of speeding, as long as the display is adapted to the detected speed. If the speeding does not exceed 10MPH, the speed is is displayed in red together with a text “SLOW DOWN”. For speedings over 10MPH, the speed is displayed in red and flashes, together with a strong alert message (TOO FAST!).
“Small speeders” do not necessarily know they are speeding. The radar speed sign will make them aware and remind them to slow down.
Drivers speeding by more than 10MPH beyond the speed limit are aware about it. In that case, the calming effect is mostly created by the fear of possible enforcement .