The precautionary principle

Dean Knight blogs:

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.
Baloney.

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. 

I call baloney on Dean’s baloney.

First of all, transport policy is not about eliminating risk, it is about balancing it – a point he admits later. Without that balance, then one would easily conclude that driving at faster than 30 km/hr is dangerous (and it is) and should be banned.

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!

Dean ignores one crucial point – if you lower the limit now, you will never ever be able to collect data on the prevalance of legally driving at a BAC of 0.05 to 0.08, and its associated risk.

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   

Yes there is a risk driving with a BAC between 0.05 and 0.05.  Lowering the limit would lower that risk. But there is also a risk in allowing people to drive at faster than 30 km/hr. There is a risk at allowing people to drive with passengers in their car, as they can be distractions.

Banning passengers and lowering the speed limit to 30 km/hr would also be “beneficial” if you only are focused on the road toll.

Of course, on the other side of the ledger, we can also say there is negligible cost associated with lowering the blood-alcohol limit. 

That is nonsense. There is significant cost associated with such a lowering. It could mean that many more people will be unable to legally drive, and in rural areas especially could even lead to the closure of pubs, where public transport is not a viable option. It may also impose extra costs on people who then take taxis home. Now you may think that is a good thing, but it is also a cost. And again I’d like to know the costs before a decision is made.

And here is the problem – we currently do not measure at all what the “cost” would be of lowering the limit, because we do not know how many people currently drive with a BAC between 0.05 and 0.08, and hence we can’t calculate what the cost will be of a law change.

I want the Government to be able to answer a few simple questions before they make a decision:

1. What is the current prevalance of drivers with BAC between 0.05 and 0.08
2. How many drivers with a BAC between 0.05 and 0.08 are involved in accidents
3. What then are the accident rates for drivers with a BAC below 0.05, betwene 0.05 and 0.08 and above 0.08
4. How many accidents and fatalities are caused by adult drivers with a BAC betwene 0.05 and 0.05

Once you have that data, then you can make a sensible decision about whether the benefits of reducing the BAC to 0.05 is worth the cost.

If you go down Dean’s path, then we will never ever be able to gain that knowledge. His precautionary principle plea, is in fact a cloak for making a decision that one could never later challenge.