Pushing the Limit

I see the police are attempting to revive the debate on a lower blood-alcohol limit again. I was originally very much in favour of reducing the limit from 0.8g/L to 0.5g/L, as I posted in this blog in August (Drinking to the Limit). I bought into the police arguments that lowering the limit would improve driver’s reaction times and reduce accidents as this accorded with the medical research data. Being an ED doctor does tend to make you quite anti-alcohol (in everybody else, at least).

Taking a closer look at the data, however, I found that, while the facts were as presented, the conclusions were by no means as certain. The arguments for lowering the limit seem to run on these lines.

1. Most other countries in the world have a lower limit. I have started with this argument as it is the weakest. Just because other countries are doing it, this doesn’t mean that we have to. I note that the countries that still have higher limits are the US, Britain and Canada. China has no limit at all. Clearly the arguments for lowering the limit are not irrefutable.
2. Even small amounts of alcohol significantly impair your reaction times. This is true, but it is a little misleading. This is the commonest argument that people give for wanting to lower the limit. However, most of the impairment caused by alcohol occurs between levels of 0.2g/L and 0.6g/L. Beyond 0.6g/L your reaction times increase quite slowly. The difference in reaction times between 0.5g/L and 0.8g/L is actually quite small and unlikely to be of significance in accident statistics.
3. The risk of a fatal crash increases with a blood alcohol above 0.5g/L. This is also true, and has more merit than the previous argument. However, this information is taken from a 2000 study (Zador PL, Krawchuk SA, Voas RB.  Alcohol-Related Relative Risk of Driver Fatalities and Driver Involvement in Fatal Crashes in Relation to Driver Age and Gender: An Update Using 1996 Data.  J Stud Alcohol 2000;61:387-95.). The study uses quite broad categories of 0.3g/l (0.2-0.49, 0.5-0.79 etc) . It is therefore difficult to determine what would be the optimum alcohol limit (although it is clear that under-20-year-olds should have a limit in the first group as their relative risk is more than 4 times greater than the first group). The figure of 0.5 may simply be an artifact due to the placing of the group limits and the real best blood alcohol limit may be o.25g/L. I am unaware of a more refined study, though there is a recent NZ study whose results I have not seen.
4. Countries that have lowered their maximum level to 0.5g/L or lower have lowered their accident rates. Again true. However, countries that have not lowered their maximum blood alcohol levels have also lowered their accident rates by roughly the same amount. The lowering seems to be mostly due to safer cars and better policing, rather than the law. Head to head comparisons of accident rates are also misleading as accident rates are determined by a great host of factors.  Lately, I have noticed people referring to “accidents in which alcohol was a factor”. Unfortunately, this is not useful statistically as it seems to be defined differently from study to study. There is an enormous difference between having a blood alcohol above 0.8g/L and ticking a box saying “I have had alcohol within the past 12 hours”  - both of these have defined alcohol as a “factor” in various studies.

I note that points 2 and 3 can still be used to make a good argument for a blood alcohol limit of close to zero (say 0.1g/L). A zero limit will cause problems with alcohol-containing medications, late night parties and measurement errors and uncertainties. I also note that there is no “halo” effect to a lower limit, as some people have argued. People who are normally law abiding remain so and drink less. Recidivist drunk drivers continue to drive with blood alcohol levels considerably in excess of 0.8g/L – they do not reduce their drinking just because they see others reducing their intake.

Restaurants have always been opposed to the reduction. A significant proportion of their profits come from the sale of alcohol. Currently a couple can split a bottle of wine and still be well within the limit. At 0.5g/L, a small person may well be perilously close to this after half a bottle of wine.  I think their argument is not without merit, given that the reduction of the limit is unlikely to save lives. It seems fairly pointless to add to the economic stresses of restaurants without a benefit on the roads.

As DPF over at Kiwiblog points out, very few accidents are caused by people at or near the limit – they are normally well over. These people will not stop their excessive drinking because the limit is lower. Note that the average blood alcohol level of a drunk driver is 1.8g/L! Most of these people have serious alcoholism and need treatment.

I know I will be called reactionary for this, but it seems plain to me that the answer to drunk driving is not to fiddle with blood alcohol limits. The answer is to get draconian with drunk drivers. I have heard of a person being fined and their license suspended for two years for their sixth offense – an offense that included driving without a license. What was the point of that? Why is drunk driving such a joke to us Kiwis? There is no point in the law being a mere punishment, it needs to be a very scary deterrent.

First offense: mandatory 6 months in jail, license suspended for five years (laugh that one off!), Alcohol rehab while in jail.

Second offense: 2 years, license revoked for good. Endorsement on credit rating to make you unable to buy a car on credit.

Third and subsequent offense: 5 years, Car you were driving confiscated and sold (including the car of anyone foolish enough to lend you one) – any residual moneys goes to victims of drunk drivers fund. 

No home detention, no fines, no PD – just straight jail time. Injuries to other people gets you bumped up a tier (First becomes second offense, second becomes third). Killing someone gets you time for manslaughter (additional 2-5 years) as well as drunk driving charge as per injury.

Until being a drunk driver is regarded as a crime rather than simply a prattish thing to do, I can’t see we will ever rid ourselves of this scourge to our country. It is obvious that all the expensive TV advertising has been ineffective in changing our thought patterns. Perhaps the heavy hand of the law may do better. 

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