Name for awareness of the probability of an event increasing the probability of it happening Before Christmas, NZ Police announced they would be enforcing a zero tolerance on exceeding the speed limit in December/January. Previously there was a 10kph grace unless a driver was obviously driving dangerously. The rationale would be that it would reduce the holiday road toll (deaths through motor vehicle accidents).

Unfortunately the road toll doubled over the previous year.

I'm aware that this could be an anomaly and is subject to many factors, however, is there a related psychological principal (perhaps something around 'suggestion') that states that if a person or population is made aware of a probability of an event, that the probability of that event happening is increased?
I believe what you are describing is known as self-fulfilling prophecy and has been well-studied.


  Self-fulfilling prophecy are effects in behavioral confirmation effect, in which behavior, influenced by expectations, causes those expectations to come true. It is complementary to the self-defeating prophecy.


It is due to an uncontrolled, positive feedback loop between the expectations of a group of people and their behavior.  It applies to a wide variety of situations, such as market panics and bank runs, to expectations of an individual's position in society.

In fact, your example describes a self-defeating prophecy.


  A self-defeating prophecy can be the result of rebellion to the prediction. If the audience of a prediction has an interest in seeing it falsified, and its fulfillment depends on their actions or inaction, their actions upon hearing it will make the prediction less plausible.


In essence, the people in your example didn't want the speed limit buffer to go away (in effect, making the speed limit lower) so the theory states that they purposely (if subconsciously) increased the rate at which they crashed to disprove the government's theory that lower speed would prevent crashes.