So the RAC says that speed cameras are a success. I say not. The RAC are correct, but then they only look at figures from 1990 onwards. This is around the year that cameras were introduced. They do not look at what was happening before that point in time.
Speed cameras make hardly any difference to road accidents overall. Accidents have been going down before speed cameras were introduced. Looking at the chart from Wiki, you could be lead into thinking that accidents dropped due to the introduction of cameras in 1991. But though that is true for the immediate period after the introduction which would be mainly due to the publicity, the general trend has not changed since the 1970s. We are now getting down to levels where reducing accidents further will require us to have a man with a red flag walking in front of cars, but some people want that to happen.
The fixation on speed ignores other an aspect of driving that are more important. That of driving to the conditions and environment of the road. So a 30mph speed limited road is too dangerous to do 30mph when it is icy or near a school or is residential. But 90mph on an empty dry motorway is very safe. But you get fined for the later but ignored in the former.
So yes, speed cameras do have a purpose. But a very limited purpose in reducing accidents. They are more successful are generating money. And if they are generating money they are failing.