18th September, 2004

Dear Economist,

I’m in the market for a new car and I was thinking of buying an SUV. What would you say were the pros and cons?
Yours sincerely,
— Vanessa Thorpe, Chelsea

Dear Vanessa,

An ordinary car will go half as far again, per litre, as the “Chelsea tractor” you are considering. Most people spend between three and four per cent of their income on fuel, so choosing the sport utility vehicle would be like putting a penny or two on your income tax. But since you are turning down the opportunity to buy a second-hand Fiat Punto, perhaps cost is little object to you.

Let us instead postulate that there are two types of Chelsea drivers: those motivated by fashion and those who desire safety. If you are seeking safety, game theory must be your guide. The safest choice depends on what other Chelsea drivers have chosen. SUVs have a tendency to flip over while going round corners, but they are a safe choice for crashing into other tall, heavy cars. Ordinary cars tend not to roll, but do not provide good protection when hit by SUVs.

There are therefore two stable equilibria, one where all the safety-conscious drivers choose SUVs and the other where none of them do. A shift in the driving habits of the fashion-conscious could presumably push all the other drivers from one equilibrium to the other. But whether style or safety is the motivating force, the advice is the same: if you feel that the tendency of the times is to buy SUVs, best to do likewise. If you feel that they are last season’s craze, get something smaller.

Implicit in this recommendation is that you do not care that choosing an SUV raises the risks to other road users. But then, why should you?

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