New drunken-driving law road-ready

BATON ROUGE -- The state's new, lower threshold for drunken driving goes into effect Tuesday, and State Police said Friday they will be ready to enforce the law.

"The change to .08 blood alcohol level will not affect how we enforce the law, but it will enhance what we are already doing to save lives on the highways of Louisiana," said State Police Superintendent Col. Terry Landry. "The effects of alcohol on a person at 08. . . . can be just as deadly as they are at .10."

People at or just over the new limit are unlikely to recognize "impairment" in themselves. Neither is it necessarily likely that their condition would be obvious to an experienced observer such as a police officer, so for establishing that a person is "over the limit" officers will probably rely more than ever on the "breathalyser". It is important therefore that people be aware of the fact that the breathalyser is notoriously inherently unreliable.

First, the breathalyser measures alcohol content in the air in the lungs, not in the blood. Since there is no uniform relation between blood alcohol content and breath alcohol content, the breathalyser employs an "average" ratio to give a reading of blood alcohol content. At worst it may register a blood alcohol content 60% above the actual value; of course it can also give a value much lower than the actual.

Secondly, the detection device is not alcohol specific, but will react to many other chemicals (specifically anything in which the methyl group is present); for example the acetic acid in vinegar. Even a person who has eaten bread will show a positive blood alcohol content even though he has had none to drink.

The problem will obviously be mitigated if officers don't proceed to a breathalyser test unless they have other reasons to suspect actual impairment, but not all are likey to follow this rule.

It is my understanding that at breathalyzer is a "rule-out" test; that is, it is not considered definitive proof of being drunk -- a blood test is required, or they cannot prosecute for DUI. If I recall correctly, breathalyzers are intended to see if the person might be drunk, or if they're suffering from a diabetic problem.

"The effects of alcohol on a person at 08. . . . can be just as deadly as they are at .10."

And the effects of .06. . . . can be just as deadly as they are at .08. And the effects of .04.... and so on. Incremental prohibition if I ever saw it, brought to you by the feds.

"It is my understanding that at breathalyzer is a "rule-out" test; that is, it is not considered definitive proof of being drunk -- a blood test is required, or they cannot prosecute for DUI."

That may be so in some states, but I don't it holds throughout the country.

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