Speeding to a conclusion

I suppose I should really say something about the mass switch-off of safety cameras.

I regard this as a really exciting thing, in fact. Not because I'm less likely to be prosecuted (there are still plenty of speed traps in Oxford), but because it will provide an excellent experiment. For years, those of us who opposed cameras claimed that the statistical evidence which purportedly supported them was illusory, while those whose livelihoods depended on them claimed that they were responsible for saving countless lives. Now, they have been suddenly and abruptly switched off in one part of the country, while remaining in use in others. We will, in time, be able to compare, directly, the change in accident and fatality rates in Oxfordshire before and after 31 July 2010, and put this alongside any change in the same rates (measured in the same way) in other counties.

This is a statistical gift to the nation and to the cause of road safety. If done properly, it could actually answer the question of whether speed cameras are a good idea or not. Swindon gives us a hint as to what might happen, but (even there) it is too early to say.

Which is why I am very annoyed by this tweet and the news story behind it. I did in fact hear the full story on the radio yesterday, and it concerned a reported who went with a BBC reporter to the site of 2 speed cameras in Oxfordshire. It seems that although the cameras are not active (they are not putting film in them) they are still switched on and therefore record the number of times they would have fired had they been loaded with film. From this, the camera operator was able to tell the BBC reporter that one site showed an increase of 88% and the other showed an increase of 18%. Asked to comment on this, the operator heavily qualified his reply by saying that if this was representative, then more people could be expected to die in accidents.

This then becomes the headline:

The number of drivers speeding past Oxfordshire's deactivated speed cameras has increased by up to 88%, a road safety partnership claim.

First, they do not claim this. They report that one camera showed an increase of 88%. Note also that they report that the other showed an 18% increase. Second, this is after 5 days, at 2 sites out of 72.

This is, therefore, hardly representative. A hopelessly short period, a pathetically small sample, and an overblown interpretation give, as ever, a lurid headline with which to bash those horrible nasty people who use cars. I hope that the research that is eventually done is reported more responsibly, more competently.

Now, as it happens, I know both camera sites. The 88% site is one which falls into the category that might politely be described as having a somewhat lower speed limit than might be expected given the conditions. The 18% site is in a 30 zone that is 100% justified. If the results are at all meaningful then it is, of course, rather interesting that drivers seem mainly to be ignoring the less-obviously-correct limit.

Perhaps we will not see the slaughter of the innocents that the safety camera partnerships predict. I hope not, for several reasons.

Update - Here's a much better suggestion...