Ex Speed Demon

I had a half-day driving course yesterday, run by the AA on behalf of the police. The deal is that speeding violators, if their offence is not too serious, can take the course instead of a fine and three penalty points on the licence. The course costs the offender eighty-six pounds, while the speeding fine would have been only sixty, but the penalty points might affect the cost of future insurance. In any case, I was happy to be offered expiation for my sins.

speed limitI found it all very interesting, and the four hours in the lecture room passed surprisingly quickly. Even though my offence had been speeding at 74 miles per hour in a 60 limit, the part that had most impact for me (pun accidental) (additional pun also not intentional) was to do with the dangers of breaking the 30 miles per hour limit on urban streets. There is a substantial decline in  survival rates for pedestrians hit by vehicles for even modest increases in speed; and stopping distances can make the difference between life and death.

On reflection, it made sense to me. Kinetic energy depends on the square of the velocity, for example, which in effect multiplies up any speed increase. For myself, I knew quite well that I had a tendency to treat a ’30’ limit as meaning “OK if the first digit of your speed is a ‘3’”. If I can apply the lesson, then the training has been a success.

In fact, of the 27 people on that course, 24 (or 88%) had been caught in a ’30’ or a ’40’ zone, and three (including me) in a ’60’ zone (none in either ’50’ or ’70’ zones). You have to be careful with that statistic, since we don’t know how many drivers exceed the limits by so much that they don’t have the option of taking the course (motorway speeders, for example).

But one thing stuck out. Of the 15 caught exceeding 30 miles per hour, 8 had been formally assigned a speed of exactly 39 miles per hour. That seems statistically improbable — it’s got to be some sort of convention, although you can only guess what it really means. My cynical guess is that it’s a way of massaging the stats.

None the less, count me newly educated and determined to go and sin no more.

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