April 12, 2010 2:00pm by David Farrar

MacDoctor on drink driving

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.

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.

And it about balancing risk to costs. If risk is the only factor we would set the speed limit at 30 km/hr and ban people from driving if they have consumed any alcohol at all.

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.

Just as there is no “safe” speed to drive at. Again it is balancing risk vs cost.

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.

It is reprehensible that you have drivers with 10 or more convictions for being plastered while driving, and they get minor slaps on the hands.

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.

This is a very worthy idea. It would probably be inefficient to make every driver pulled up randomly undergo such a test, but one could do a screening test for alcohol and drugs, and any non-zero response has to do the impairment test.

I doubt the Government will go this way, as Government like objective tests, not subjective ones. But it could go a long way towards having a less arbitrary system, where people are punished only if they are actually impaired to a level which presents an unacceptable risk.