2 reasons, remembered from a lawyers lecture on the subject at uni, years ago, in the UK.
Some people produce small amounts of alcohol in their gut. It’s generally not much (more becomes auto brewery syndrome) but not zero. This can blip the test up slightly, even when they haven’t drunk.
The awkward fact that a small amount of alcohol actually improves driving. It’s somewhere between 1/4 and 3/4 pint of beer. It’s also the reason alcohol is considered a performance enhancing drug in some olympic sports.
The limit is set high enough that there is no arguing these points in a court. It also covers the residual alcohol in people’s systems the morning after. It’s well into the point where all but the heaviest alcoholic will definitely be impaired. That lets them use blood alcohol as a proxy for impaired driving due to alcohol.
On a side note. I know someone who blew red on the breathalyser. He knew something was wrong, since he has been teetotal for 20 years. He got arrested, only for the blood test to show 0.0. The police were quite confused, but let him go. It turned out, he had (unthinkingly) eaten a liqueur chocolate before being pulled over. It was enough to mess up the breathalyser.
2 reasons, remembered from a lawyers lecture on the subject at uni, years ago, in the UK.
Some people produce small amounts of alcohol in their gut. It’s generally not much (more becomes auto brewery syndrome) but not zero. This can blip the test up slightly, even when they haven’t drunk.
The awkward fact that a small amount of alcohol actually improves driving. It’s somewhere between 1/4 and 3/4 pint of beer. It’s also the reason alcohol is considered a performance enhancing drug in some olympic sports.
The limit is set high enough that there is no arguing these points in a court. It also covers the residual alcohol in people’s systems the morning after. It’s well into the point where all but the heaviest alcoholic will definitely be impaired. That lets them use blood alcohol as a proxy for impaired driving due to alcohol.
On a side note. I know someone who blew red on the breathalyser. He knew something was wrong, since he has been teetotal for 20 years. He got arrested, only for the blood test to show 0.0. The police were quite confused, but let him go. It turned out, he had (unthinkingly) eaten a liqueur chocolate before being pulled over. It was enough to mess up the breathalyser.