Safe Speed Forums

http://www.numberwatch.co.uk/2005%20July.htm#speed

The epistle of Paul to the innumerate

The inevitable about turn on speed camera policy was heralded by a full page article in The Times – Speed camera U-turn as 500 sites rejected. Why was it inevitable? For the simple reason that the Government’s policy was to promote an exponential growth of camera numbers.

You do not need to be a mathematical genius to be able to deduce that if you feedback a fixed proportion of the income from speed cameras to buying more speed cameras, their numbers will increase exponentially. It is an example of the most basic form of differential equation (first order) that used to be taught in schools. Eventually you will have more cameras than people. It had already reached the absurd level at which cameras were looking for sites rather than sites looking for cameras.

The fact that the subsidiary article in The Times actually mentioned Regression to the Mean is a breakthrough for real science and a triumph for one lone web campaigner. Paul Smith on his Safe Speed web site has pursued the illogic of speed cameras with a great persistence, first noted here in January 2003, which has finally paid off.

Officials might claim that he had nothing to do with the decision, but there is evidence otherwise. When your bending author was cited on Paul’s web site as having supported the point about regression to the mean, it resulted in a letter from a Government official, via the University, asking whether the claimed support was valid. There was an implied belief that it was an invention. The reply confirmed the belief that the criticism based on Regression to the Mean was correct.

Mathematics aside, any policy that mindlessly pours money into an activity is going to produce a cohort of parties with an interest in promoting it; most notably the egregious Richard Brunstrom and his ilk, but also those for whom it provides a nice little earner. Speed cameras provide one of the largest contributions to the Number Watch inbox from all over the world. They owe their birth to the bureaucrat's distaste for the Sorites paradox and love of thresholds.

Incidentally, The Times article carries an interesting graphic with a fine example of chartmanship in the form of a suppressed zero.

15/07/05

(The original article is liberally sprinkled with links, and I don't have the time to reproduce them right now.)

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety