Friday 27 September 2013

Drink driving limits revisited

A member's bill proposing a reduction in the drink driving limit was drawn from the ballot.

Last year, I ran some ball-park numbers on what would be needed for it to make sense to reduce the drink driving limit from 0.08 to 0.05. While you would have some reduction in crashes among drivers in that range, you'd also have losses in consumer surplus among drinkers who would have driven home safely at 0.07. My very rough conclusion was that if those in the .05-.079 range suffered reduced consumer surplus of less than $4 per night out, then the policy could make sense, and if those in that range suffered losses greater than $4 per night out, then the policy would fail.
Let's suppose that the costs of non-fatal accidents are on par with the self-imposed fatality costs incurred by drinking drivers so the $4 is ballpark ok (but note the overestimate problems as it includes people in the 0.08 to 0.105 range). Do you expect that most people enjoying a night out would be willing to accept $4 to be subject to a 0.05 rather than a 0.08 limit? Don't tell me "Oh, I would, because I never have that much anyway." This question isn't for you. This question is for those who go out for the night and either worry that they've exceeded 0.05 or know that they're in the 0.05 to 0.08 range. As you walk into the bar someone offers you $4 and says "You can have this $4 if you can guarantee that you'll stay under 0.05 tonight." If most drinkers subject to the risk take the $4, and if the $4 is ballpark correct, then moving to 0.05 makes sense. If you'd have to offer them more than $4, then it's a value-destroying proposition.
The numbers were pretty rough. I was then waiting for the folks at MoT to provide me with some more recent figures on the proportion of drivers on the road who are in the .05-.08 range. They never got back to me after promising me the numbers, but I didn't pester them either as I got busy with other things. It looks like I'll have to start pestering again so I'll have a chance of running the numbers before the Bill is debated.


  1. Please get in touch with Don Bevin or Morgan Fahey, both Christchurch men, whose work was the inspiration for our first Blood /Alcohol ratio limits..
    Their preferred level was >120 and they had good reasons for that level.The most likely reason MoT won't come back to you is their own figures will show they are being silly; the levels recorded in big prangs are way over the .167 which is the definition of "Physically drunk". The proposal is rather like saying that if you drive at over 30 kph we'll assume you intended to exceed the speed limits and treat you as a criminal.

  2. kohicbs poster

    Professor Bevan before he died had long given up on the alcohol / police industry.
    He is on record as realizing nothing would change their focus on results based prosecutions.
    As you know every accident or death with any measure of alcohol, is an “alcohol incident”
    I will go further, the Police do not have the numbers, they can not monitor driving and they know it.
    People like Prof Bevan and my brother Prof Russell Scott decided to put their energy into human metabolism and the food diseases.
    On another matter Mr Eric your site is hard to get into from overseas.[ Thailand]
    takes ages, whereas I can hit Farrar in 30 seconds,
    Paul Scott