They recently installed a new radar at a local highway, right at the beginning of a speed limit.
Everyone sticks to the speed limit now.
A different section of the highway has "section control". (Cameras at the beginning and end of a section that record license plates and determine average speed). Nobody speeds there either.
With todays technology it is trivial to enforce speed limits everywhere, and people really do stick to the speed limit if they know that there are consequences.