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ASK A COP: Impairment is in the eye of the drinker

QUESTION: I was surprised to read how little alcohol put Karen Stampfli over the limit, as revealed on the cover of North Shore News Aug. 1 (Lessons from a Drinking Driver).


I was surprised to read how little alcohol put Karen Stampfli over the limit, as revealed on the cover of North Shore News Aug. 1 (Lessons from a Drinking Driver). Is there some way we as individuals can test ourselves to know when our own drinking (or that of our house guests) is over the limit? I've seen pocket breathalyzers for sale, but these may not be accurate or calibrated the same way as police breathalyzers.

Can you share the manufacturer, brand name, model and approximate cost of the devices used by the police? To your knowledge, have ICBC or the police considered a program allowing bars and restaurants to obtain a reliable device so patrons can test themselves before leaving in their cars?

Thanks Charles Lindsay North Vancouver

Dear Mr. Lindsay:

Thank you for your question.

To be frank, there are no foolproof, reliable ways to do this, the reasons for which are actually quite complex.

Factors involved in the onset of impairment due to alcohol consumption are manifold, and the effects of impairment on the body are multifarious. Obviously, I can't comment on any case in specific, but although I'm neither a medical doctor nor an impaired driving expert, I have gleaned some knowledge on the topic over the years, and there are a few things I can tell you about driving and alcohol.

The effects of impairment can be divided into two categories: psychomotor, which involves how the brain controls the body, and cognitive, which refers to the way the brain processes information. Each of these categories is affected by the consumption of alcohol.

Eye movement is particularly vulnerable to alcohol consumption. For that reason, one of the best tests for impairment relates to tracking eye movement. Have you ever heard of an officer moving a pen in front of a driver's eyes? She's testing their movement. Put simply, without alcohol in the body the eyes track smoothly, whereas after alcohol consumption the eyes move haltingly.

One of the most complex actions involved in driving is the act of steering. Hand-eye coordination allows a driver's brain to process visual stimuli that will cue him to execute subtle physical manipulations of the steering wheel. Alcohol slows this process, and when this effect is superimposed on the diminished eye movement I've described, significant impairment in steering ability starts to occur.

But let's not stop there; we haven't even started talking about the cognitive tasks involved in driving. Alcohol impairs nearly every aspect of information processing that takes place in the brain. The brain's field of attention narrows, reaction times slow, and the brain tends to access fewer sources of information in making decisions.

Perhaps most significant is the effect alcohol has on the brain's ability to coordinate the host of skills required for safe, attentive driving. A brain impaired by alcohol has a much more difficult time dividing attention between numerous tasks.

Take a moment to think about the multitude of considerations we make while behind the wheel, from our position in our lane, to the vehicles around us, to traffic lights and signs, weather conditions, pedestrians, how tired we are, how hungry we are - the list goes on. And that's saying nothing about that annoying song on the radio, or the kids fighting in the rear seat, or, lest we forget to go there, that cell phone in the cup holder beside you.

Driving creates a perfect storm inside the brain. Alcohol upsets the delicate balance needed for this near-Herculean task of fine-tuning physical reactions to an ongoing deluge of varying data.

But back to your question about the use of a reliable device. What many people do not know is that the relationship between a person's blood alcohol content and their level of impairment may vary due to a host of factors. These include how much alcohol has been consumed, the rate at which it is consumed, the absorption rate, a person's lean body mass, weight, gender, metabolism, age - I'll stop there because I think the point is made.

Because of this, although a breath sample device can tell a good deal about a person's alcohol consumption, it cannot fully account for the host of factors involved in determining the level of a person's impairment. This is one of the reasons impaired driving charges can be very difficult to prosecute in court, and why we often hear of drivers getting off on "technicalities."

It is also the reason no bar or police agency that I know of would recommend this as a reliable way to determine one's ability to drive.

And so, in answer to your question specifically, please don't believe you can depend on one of these devices alone to tell you if you've had too much to drive. Aside from their inherent unreliability, the collection of factors involved in making that determination shouldn't be narrowed to one breath sample test. My best advice is to choose one person who won't drink, and then make sure she drives.

To drink even a small amount of alcohol and then drive can be a fine line to walk; fall on the wrong side, and the consequences could be dire. Sgt. Peter DeVries, North Vancouver RCMP Follow Peter on Twitter: @ rcmpdevries. If you have a question for Ask a Cop, email it to editor@