The drink driving limit

The national road policing manager has called for the legal blood alcohol limit to be reduced from 80mg per 100ml of blood to 50mg per 100ml of blood.

As with all things, one needs to look at the benefits and costs.

The benefits are fairly obvious. There would be some reduction in accidents and deaths caused by drivers affected by alcohol. However it would be pretty minor as the vast majority of fatal accidents involving alcohol are not in the 50 – 80 mg range but well over 80 mg.

Looking at MOT research there were 100 fatal crashes, killing 155 people, involving alcohol in 2005. They estimate a social cost of $660 million from

Quite fascinating is the licence status of alcohol affected drivers in fatal crashes. Only 43% have a full licence, with 27% on learner and restricted and 15% not legally licensed at all. So lowering the blood alcohol for drivers on a full licence will only affect a minority of fatal crash cases.


Now this graph stolen from the MOT shows very clearly where the problem is. The vast majority of crashes are when people are double or more the legal limit. The numbers in the 51 – 80 range are in single figures, and this is for over three years. I’m somewhat stunned by the numbers who are triple the limit!

So the benefits of a reduction to 50 mg are not particularly large, compared to the overall problem.

Now let us look at the costs:

A 50 mg limit would mean a couple could no longer safely share a bottle of wine over dinner. It would mean you couldn’t even have two or three drinks legally after work unless you get picked up or like me can walk home.

Overall it would seriously reduce normal everyday socialising, without significantly affecting the drink driving problem which consists of young drivers or repeat and disqualified drink drivers who are generally twice the existing limit anyway.

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