Drink Driving Limits

The Herald reports:

Transport Minister yesterday described existing legal alcohol limits for drivers as “ridiculous”.

Speaking to a conference of traffic experts in Auckland, Mr Joyce said he could drink three-quarters of a bottle of wine in 90 minutes yet still have every chance of being under the legal alcohol limit for adult drivers.

Shouldn’t the test be how impaired one would be at a blood alcohol level, as well as what that means in terms of actual drink.

I see this going the same way as the cellphone debate – a kneejerk reaction with little proof it will actually make a difference to crash statistics.

The Dom Post has a story today that quotes overseas reseach suggesting the cellphone ban will not lead to safer roads – it will just lead to people getting fined for continuing to use their cellphones.

I kept asking on this blog if anyone can quote empirical evidence of a cellphone ban actually leading to fewer crashes, rather than greater fines, but no-one has done so.

Anyway back to Steven Joyce:

But he said heavy advertising when the existing adult limit of 80mg of alcohol per 100ml of blood was introduced in 1978 had made it difficult for him to gain popular acceptance for a further cut.

“A huge amount of advertising was done at the time which said it was just a couple of drinks and then one an hour.”

The result was a popular misconception that reducing the limit to 50mg – one of 61 ideas suggested in a Ministry of Transport discussion paper – would restrict motorists to little more than one standard drink if they wanted to drive home.

I don’t think that, but the rough test for me is that a couple should be able to share a bottle of wine over dinner, and not be breaking the law by driving home afterwards.

A bottle is almost eight standard drinks.

The discussion paper gives six drinks as the allowance for a man of average height and weight. For a woman, the limit is four drinks.

It says a limit of 50mg of alcohol, based on Australian guidelines, would allow an average man to have two drinks in the first hour and one an hour thereafter.

And presumably a woman would be two thirds of that. So let us say a man would have five standard drinks and a woman three standard drinks from a bottle of wine. At a 50 mg limit they would be breaking the law unless the dinner lasted four hours.

But that isn’t een the most important test. The question that (in my opinion) the Minister should ask is how many accidents are caused by drivers with blood alcohol between 50 and 80. In other words how many crashes would potentially be prevented if the limit was lowered, and how many people would be criminalised for having a bottle of wine over dinner. Again I’d like non-emotional study of the benefits and costs of any lowering.

This 2007 report from Transport on blood alcohol levels of drivers killed in car crashes finds the following:

  • 60 drivers found to have a detectable level of alcohol (above 30), and 137 had under 30
  • By far the most common level (36/60) had a level of 200 – 300 – around three times the legal limit
  • Only three drivers were marginally above the limit (80-100) and they were all under 25 so in fact they were well over their limit of 30
  • Only two drivers were in the 51 – 80 range

So most drunk drivers who end up dead are totally plastered. A lowering of the limit to 50 would possibly result in one less fatal crash every six months.

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