Fit To Drive

By Jim McVeagh 10/04/2010

Once more the media appear to be wading in to the campaign to lower the legal driving limit for blood alcohol to 0.05%. Strangely, they quote the recent spate of road traffic fatalities as if this somehow bolsters their argument. This is simply lazy journalism. There is plenty of evidence that lowering the legal Blood Alcohol Concentration (BAC) reduces accident rates, injuries and fatalities in an almost linear fashion (at least below about 0.1%). Here is a link to the very latest meta-analysis. Click on the Table/Figures tab and look at the thumbnail of figure 5 (you will have to purchase the article if you want the enlarged figure – but you can clearly see the trend).

The point is that the effect of alcohol is fairly linear. In fact, there is evidence that the largest deterioration in performance occurs at quite low levels of intoxication (0.01-0.03%) but this does not initially translate into increased accidents (One assumes that the deterioration – although large proportionately – is still not enough to cause a noticeable increase in risk). Because the increase in risk is quite linear, it follows that the setting of  a new BAC at 0.05% is entirely arbitrary. Indeed, the Japanese have shown that dropping the limit from 0.05% 0.03% produces a significant drop in accident and fatality statistics. It will therefore not be long after a drop to 0.05% that people (particularly ED doctors who bear the brunt of traffic accident injuries) will be calling for a further drop. It is not logical to go to all this trouble to fix the legal BAC at yet another arbitrary limit. There is no “safe” level of drink driving.

Worse still, the problem is actually not the amount of alcohol in your blood stream, but the degree of impairment when you drive. While there is statistical correlation between accidents and alcohol, alcohol is by no means the only reason why a person may be driving-impaired. Cannabis intake markedly increases driving impairment, as do most of the sedative and psychotrophic drugs. Some normally benign drugs increase drowsiness and decrease driving ability in the presence of a small amount of alcohol. Even individuals with the same levels of blood alcohol will have differing levels of impairment, depending on their ability to compensate for alcohol intoxication (but note that the reaction time of said individuals is still reduced to the same extent – they are just better at compensating for it).

The point here is that an arbitrary limit for alcohol intoxication is inadequate for determining whether someone is safe to drive. Even at a zero level of alcohol, other drugs may make the driver decidedly dodgy behind a wheel. It is also doubtful that any movement of the BAC limit, even to zero, will make any difference to the kind of people who get behind the wheel of a car with a BAC 0f 0.18%. As I have posted before, the only solution to that kind of fool is to change the current drink driving laws from a minor punishment to a draconian deterrent.

MacDoctor has a somewhat radical suggestion. Let us scrap the legal limit for alcohol altogether. Instead, we should substitute a legal requirement to be “fit to drive”. Should you be stopped at a police checkpoint and the cop has any reason to believe you may be impaired in your ability to drive (including checking your breath alcohol), he can insist that you take a “fit to drive” test. Failure (to take or pass the test) will get you arrested. The test could be administered using driving simulators in the back of a police van (basic tests administered by cops – such as walking a straight line – are simply too imprecise).

The advantage of a “fit to drive” test is that it catches all the impaired drivers, not just the ones impaired by excessive alcohol. It also avoids the problem of the margin where the person with the BAC of 0.052% is carted off to jail, despite being only mildly impaired, and the person with the BAC of 0.048% is let go, despite being high on cannabis and a liability on the road. It also standardises the drug tests that the new drug driving laws propose – making them considerably more objective. It will also prevent people from using portable breathalysers so that they can drink “to the limit” regardless of how capable they are of driving.

Some capital investment on the machines to test people will have to be made. I suspect you will find that the investment will be recuperated in reduced hospitalisations alone, let along the enormous ACC rehabilitation bill that drink-and-drug-driving causes each year. All that it requires is the political will to step away from conventional thinking and try an new approach.

Are you reading this, Mr. Joyce?

Related posts:

  1. One for the Road
  2. Drug Driving
  3. Driving Impaired