Agreed. But I would think that a speed trap would slow some people down, not all people. Lots of reasons for that, such as people unaware there was a speed trap there previously, people forgetting, etc.

I know that areas in my town that are well known for speed traps definitely have a lower occurrence of people speeding. On a neighborhood road near my house we had a really bad problem with speeders. Over the course of several months, there were numerous speed traps. Today, there are less speeders than before.