Steve Chapman

Under a tighter BAC, the same number of cops will be chasing a lot more offenders. An officer who is busy arresting someone with a .05 level, who poses a small danger, will not be able to arrest someone with a .10 or .15 level, who poses a huge danger.

Forgotten in these number-crunching exercises is the effect on the trivial matter of human spontaneity and enjoyment. NTSB may place a zero value on the pleasures of social drinking, but social drinkers don't. In any cost-benefit analysis, the loss of a largely harmless pleasure deserves inclusion.

Not only that, but the cost of a stricter policy is greater than it may appear. When you lower the limit, you deter not only forbidden levels of consumption but permissible levels. Why? Because most people don't care to be anywhere close to the line.

They don't travel with Breathalyzers and want to be absolutely sure of not being arrested for DUI -- which carries not only legal penalties but social disgrace. If this were a constitutional right, we'd be talking about a "chilling effect."

It may come as a surprise to hear that the organization that deserves much of the credit for raising public awareness of the problem, Mothers Against Drunk Driving, has declined to endorse this proposal. It prefers to focus on greater efforts to enforce existing laws, while requiring ignition interlocks for every DUI offender.

NTSB acknowledges this last policy would save some 1,100 lives per year -- far more than a lower BAC would save. It also has the virtue of disabling the few guilty without inconveniencing the many innocent.

In a free society, trying to reach zero carries too high a cost. Better to settle for making progress.

Steve Chapman

Steve Chapman is a columnist and editorial writer for the Chicago Tribune.

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