Faulty logic on fuel efficiency

JEFF JACOBY'S conclusion that greater fuel efficiency in cars necessarily increases dependence on foreign oil is dubious, especially because it rests on faulty reasoning (''The paradox of fuel efficency," op ed, Sept. 21). He argues that as computers have become more efficient, our use of them has increased, and he concludes that the same must be true of cars.

The difference, of course, is that computers have uses not confined by physical limits like geography and can constantly be applied to new tasks: complex calculations, writing, communications, household management, etc. Cars, on the other hand, serve primarily to carry us from point A (home) to point B (work, the grocery store, etc.). No amount of fuel efficiency will, by itself, extend the distances between our homes and our offices.

Jacoby's theory would work if lower fuel efficiency encouraged behaviors that reduced car use. But during the past 20 years, an overall decline in miles per gallon has been accompanied by longer commutes and more urban sprawl. Of course, gas prices have fluctuated during that period, but the trend indicates that car use is affected by more complex factors than mere efficiency. People's behavior isn't always as logical as economic theory suggests, and driving plays a role in American life quite different from other forms of energy consumption.

Jacoby's argument fails to take these facts into account.

JOSH MICHTOM, Somerville