5 January 2011

Alcohol, driving and the precautionary principle

- RadioNZ: "Joyce still not convinced about lower alcohol limit"

RadioNZ reports that Minister of Transport, Steven Joyce, says "more evidence is needed before the Government will consider lowering the general drink-driving limit".  Others such have David Farrar have echoed the claim that specific evidence is needed that lowering the drink drive limit will have an instrumental effect on the number of road deaths and accidents.


Yes, changes to laws should be justified.  But, no, the justification need not be specific evidence.

Both Joyce and Farrar are ignoring the precautionary principle.  In general terms, this principle says that, in relation to risky activities where there is scientific or empirical doubt about the nature and extent of the risk, policy- and law-makers should favour the course of action which avoids the risk.  That is, in the face of uncertainty, the burden shifts to those undertaking the risky activity to demonstrate it is not harmful.  This principle is especially common-place in areas such as public health and environmental law; for example, it is specifically recognised in s 32(4)(b) of the Resource Management Act 1991.

So, we know that drink driving is a risky activity.  That's why we prohibit driving above the current blood-alcohol level (80mg).  If there's doubt about whether driving while above a reduced limit of 50mg (which I not sure there is doubt about when looking at international practice), then the precautionary principle would favour lowering the limit anyway and collecting data to demonstrate it is not risky or has no instrumental influence on road accidents and deaths - not the other way around!

Ultimately, these things involve a cost-benefit calculus. There are seldom king-hits in law- and policy-making. A balance must be drawn.

Joyce and Farrar et al are, however, underplaying the benefit (risks avoided) of lowering the limit by proclaiming uncertainty about their nature and extent.  In this context, though, we're entitled to assume there is a risk associated with driving with a blood-alcohol of over 50mg, unless evidence shows otherwise.  This means, for the purpose of the cost-benefit calculus, we can assume lowering the limit is beneficial   

Of course, on the other side of the ledger, we can also say there is negligible cost associated with lowering the blood-alcohol limit.  First, there is no social utility associated with driving having drunk that amount of alcohol.  Secondly, a limit of 50mg still allows a buffer.  It avoids criminalisation of behaviour which is not risky.  Officials have confirmed that it will still allow folk to have a drink or two before driving without risking being over the limit.

This is a no-brainer.  Our intuition tells us lowering the limit to 50mg is a sensible measure.  It's supported by sound principle.


Matthew Proctor said...

This line of reasoning worries me. Although there is nothing specific in it for me to object to, boundary issues are obvious. What's to stop us saying that driving over 5mg/L is similarly 'risky', and should therefore be banned until it's demonstrated to be safe?

Also, while it's obvious there is no particular social utility to driving while intoxicated, there IS utility gained (it's private, but that's no reason to discount it) by people in being intoxicated, and in driving. That these effects don't compound shouldn't count against them.

Dave Guerin said...

I agree with Matthew. Laws are not based on simply assessing social costs and benefits but private costs and benefits as well. There is a substantial private cost to lowering the limit, which makes the issue complex, rather than a no-brainer.

Granny Morris said...

Empirical evidence suggests that a maximum driving speed of{any number below 100} kph will result in less deaths on the road than the current 100kph, due to reduced impact trauma.

By your reasoning Dean, it is a no-brainer to reduce the maximum driving speed limit to that number.

In fact, I suggest 8 kph would be as good a number as any other, and the impact at 8 kph would be negligible for all but the smallest child. There is of course no social utility in being able to get between Wellington and Palmerston North by road in less than 24 hours, although I suspect that those travelling south may have a different viewpoint.

There would of course need to be a better way of monitoring the limits than at present. I suggest that the appointment of designated flag carriers, each equipped with a red flag and walking ahead of the line of traffic, would be the most effective means of providing this.


Dean Knight said...

Matthew and Dave:

I acknowledge these things depend on an assessment of costs and benefits (whether public and private). The point I was making was that those ignoring the precautionary principle are effectively arguing there is no benefit from a lower limit because the benefits are not "proven". I'm essentially trying to rebut that proposition.

But on the (largely private) cost of a lower limit, I accept that needs to be feed into the calculus. I don't accept there are significant private or public costs to lowering the limit to 50mg. It would be a different story if it was lowered to even more, as then it would create more costs for folk. We're talking about driving whilst quite boozed - I think the MoT said above 2 drinks in the first hour and 1 drink thereafter? The affect on people's liberty isn't significant in my view.

Dean Knight said...

Granny Morris

That's a false argument. You've miss my point.

1. We have lots of empirical data on the effect of the speed limit. We don't need to assume here.

2. Lowering the speed limit is something that has a siginificant (private and public) adverse effects. There is utility in getting from A to B quickly. That needs to be factored into the mix.

Granny Morris said...

I don't think I missed your point at all.

You will recall that the Police used a less extreme version of my argument to justify their recent precautionary holiday period reduction of their extra-statutory speed tolerance, despite the empirical evidence from 2010 being downright contradictory.

The reality is that it is not those who are marginally under the current limit who cause the significant danger, and bring into play the precautionary principle; it is those who can and do ignore any limit whatsoever, and drive whether licensed or not, that cause the damage.

It seems to me that your proposal simply reflects a desire to be seen to "do something", rather than any concrete attempt to solve the bigger problem. It's clearly far easier to criminalise a section of the community without sound evidence, than to address the entrenched problem of hardened drink drivers.

I wonder Dean, what precaution you might advocate as appropriate to deal with that greater menace?

ben said...


Dean, this is a howler. Of course there is very substantial cost with a lower limit. More people will be convicted. This is costly, both in the conviction and, by its nature, in the punishment meted out. Millions of glasses of wine will be forgone at meal times because people cannot be certain a single glass at the lower limit will not put them over, and the consequences for being over are severe. The enjoyment forgone is a cost.

Now those costs may be justified by the benefits of a lower limit, but it is flat out wrong to say those costs are negligible.

I'm sure I speak for many New Zealanders when I say I value the ability to have a glass of wine after work safe in the knowledge that one will not put me over and risk my career. For many people that is what will be lost by the lower limit.

ben said...


I've just read this comment from you Dean - I hope you won't cite that in response to my point above. This is a guide, not a guarantee. It takes no account of uncertainty, and the rational response to severity of penalties for even a minor breach of the brightline limit: the rational response is to stay well away from the limit. What the lower limit does is take away the safe harbour I suspect most people feel in having a glass before driving.

Anonymous said...

Dean, you say that "we know that drink driving is a risky activity". Actually we don't know that at all. Certainly if a driver is drunk, the odds are greater that the driver will be involved in an accident…but you didn't say that.

You could of course argue that driving is a risky activity. You should bear in mind that many accidents - the vast majority I suspect - involve drivers who have consumed ZERO alcohol. What should we do about these drivers - the sober ones that have accidents?

One final point: Police and transport agencies have undertaken many advertising campaigns over many years. Using a cellphone while driving is now illegal. Cars and roads are generally better than they were 30 years ago. But the road toll remains stubbornly high. What effect will lowering the BAC have? I suspect very little...it is surely up to those advocating a law change to explain why the law needs to be changed. Out of interest, if the BAC were to be lowered to 0.5 and subsequently it was shown to have little effect on either the road toll or the accident rate, would you favour repealing the law so that the BAC was 0.8?

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