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A PHYSICIST WRITES . . .
(September 2009)
I am writing this column in the silly-season month of August, so let me report on some examples of motoring silliness.
In 2002 the Stockport Road Safety Team put out an advertisement on the local radio station. I have just discovered it, stored on the internet. It starts with a drum roll, then we hear an authoritative male voice: To balance well is an incredible skill. A tightrope-walker may train for many years before she dares go out ... without the net. The audience gasps, and a seductive female voice takes over: If you think you’re a skilled driver, then try keeping the needle of your speedometer on 30 miles per hour. It’s a precise balancing act that requires practice, but please stick at it — it’s the true test of a good driver.
Not surprisingly, within hours of its first outing the advert was taken off in response to complaints, plus this comment from someone: “I tried driving as you suggested, on my way to work. It is indeed a tightrope balancing act and takes great skill. Roundabouts in particular are a challenge at this speed, especially in the wet. Also, parents may complain about the way in which I now race past the local school. Still, as long as I’m doing the right thing and sticking to your speed target, I feel I have the moral high ground.”
That’s mainly what was silly, of course — presenting the 30 limit as a target, rather than as a maximum, with road conditions and other factors governing your actual speed. But the advertisement highlighted something else too: however safe a driver you are, you need to keep an eye on the speedometer to ensure that you don’t exceed the limit. Some would say this itself is a silliness. If we had sensible and respected ‘guideline’ limits instead of rigid ones, so that drivers could give full attention to what’s ahead, might the roads not be safer?
Well, that won’t happen, so here’s an alternative silly (or maybe not so silly?) idea that originated in the USA: first, researchers found that a house advertised at a ‘precise’ figure like $488,500 will very likely sell for more dollars than if the asking price is slightly higher with more zeros, say $490,000. This seemed to be because the latter amount is assumed to have been rounded up and so will be negotiated down harder. Then later, someone suggested that drivers might be inclined to respond to speed limits in a similar way (but in the opposite direction). In other words, people might take notice of them and actually drive more slowly if, for example, the round-number 30 mph limit was raised to 32!
Which brings me to speed cameras ... I haven’t researched this properly (after all, it is August) but I believe there’s a general rule that cameras are installed primarily at places where a certain ‘high’ number of accidents have occurred in the course of a year. Perfectly sensible, at first sight. But we should ask why the number was high in a particular year: was it because the location actually became more dangerous, or because the random variation that you get in all such numbers just happened to result in an ‘exceptional’ accident rate that year?
If it’s the latter, then guess what will happen the following year (regardless of any camera): the number will almost certainly fall back towards the long-term average rate, or quite possibly below it! The technical term for this statistical effect is regression to the mean (which seems to ignore the possibility of falling below it, but never mind).
Now it’s not too difficult to allow for regression when analysing the numbers. But in some people’s opinion the authorities don’t always do this properly. And if they succumb to pressure and erect a camera anyway, who will dare to argue afterwards that it wasn’t responsible for the observed fall in the number of accidents? Thus it is that the yellow-painted boxes proliferate.
At the Winnersh Triangle exit from the A329M near Reading is a giant new off-road sign-panel designed to give the impression that WT is the gateway to the future. On it, an illuminated moving-message strip supplies information about the WT industrial estate (including its temperature) in letters that are barely readable. All this confronts drivers across a tricky roundabout, surrounded by long-term roadworks to add to the hazards. What a contribution to road safety...
Last spring I described to you (with some difficulty) an extraordinary mix-up of double-arrow priority signs I had discovered in rural Sussex. A reader capped this, I would say, by sending me photos of a simple suburban traffic-calming bottleneck in Bucks which featured just one of each sign — the round (Give Way) and the rectangular (you have Priority) — fixed back-to-back ... except that each sign was mounted upside down and had the other one’s instruction plate attached below! Apparently it took more than a year of complaining to the council to get this put right. And as my informant said, imagine all the stages the error presumably passed through: commissioning, authorizing, installation and finally inspection.
In July I speculated on the complexities of the car I shall have to face buying one day soon. But what would my ideal car be like? Make it simple, cheap and cheerful, but solid and reasonably comfortable; let it be powerful enough but economical; fit it with bolt-on standardized bodywork for quick repairs; give it lights that tell me when they’ve failed and which are then simple to replace; and build it around a small but modular chassis that allows extra sections to be easily attached for carrying passengers and luggage. Or am I just being silly?
Peter Soul
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