Booze and driving don't mix but a zero blood alcohol limit isn't the answer

The Royal Australasian College of Physicians wants to see blood alcohol limits for Australian drivers drop from .05% to .02% and then zero.

Don’t get me wrong, there is a good argument for lowering the blood alcohol driving limit in Australia to zero. It sends a very clear message that alcohol and driving just don’t mix – and they don’t. Alcohol influences brain function, behaviour and performance on a range of tasks and there’s certainly good evidence that alcohol can impair a person’s ability to do complex tasks like driving a motor vehicle.

But a zero-tolerance approach is unlikely to curb the behaviour of individuals who choose to drink then drive.

How many road accidents involve alcohol?

Historically, road toll statistics have been used to support a hard line against drink drivers. In the 1990s, about one-third of all fatal traffic accidents on Australian roads were associated with drivers having an illegal blood alcohol concentration (BAC).

Our most recent crash data continue to highlight the dangers of combining alcohol and driving, though the proportion of fatalities linked to alcohol has declined. Alcohol was implicated in around 15% of fatal crashes in New South Wales between 2013-2015 and more than 20% in Queensland between 2014-2015.

The most catastrophic accidents involving alcohol are associated with mid- to high-range drink-driving.

Queensland crash data for 2011 show that 76% of all drink drivers involved in fatal crashes had a BAC between .10% and .24% (between two and almost five times the legal BAC limit). Only 4.4% (two cases) of fatal crashes involved a driver with an alcohol limit below .05%.

Fatal crash data from NSW show that, in 2012, only five out of the 49 drivers (where a BAC was registered) had a level below the legal limit. Of these, three were aged 17-20 years (and were likely to be on their P plates, where zero alcohol legislation already exists).

So most people who die drink-driving (or cause other casualties) are well over the legal BAC limit. Perhaps it’s because these people never cared about the legal driving limit in the first place. Or maybe they only care about themselves, not the safety of other road users.

A zero-tolerance alcohol approach is unlikely to influence this irresponsible behaviour.

The case for and against

Of course, you could argue that a zero-tolerance approach may stop people from ending up over the limit, because they would choose not to drink then drive in the first place.

One of the strongest reasons for a zero drink-driving alcohol limit would be to provide a “no room for error” approach. The effects of alcohol are not uniform across all individuals and it can be difficult to judge your own BAC after having a few drinks. Yet this is what we expect people to do: have one or two drinks and predict if they are below the legal limit before hopping behind the wheel.

Many factors influence a person’s BAC after drinking. The amount of alcohol or type of drink consumed, the person’s age, gender and weight, their drinking history and whether they have eaten are all potential factors. Even when all of these factors are controlled for in research studies, people still often report different ratings of intoxication and impairment at the same BAC level.

A zero-alcohol approach would certainly save the confusion.

But millions of people do the right thing each and every day and a move to zero tolerance would clearly affect all the people who drink responsibly and drive home safely.

Fatigue, lack of sleep, or dehydration also have the potential to affect cognitive skills to similar levels as a person blowing .05%. Fatigue is implicated in around 17% of all fatal vehicle accidents.

But it seems inconceivable to enforce a minimum number of hours of sleep or a certain hydration status before driving (both of which could be objectively determined at the road side) across the entire population.

Instead, we ask people to take responsibility for their own actions and ensure that they aren’t driving tired.

The same goes for alcohol.