Drink driving limits – experts respond

The Government plans to lower the legal blood alcohol limit from 80 to 50 milligrams of alcohol per 100 millilitres of blood for drivers aged over 20.

The new legislation is to be put before parliament before the end of the year.

The new regime will impose civil infringements on drivers with between 50 and 80 milligrams of alcohol per 100 millilitres of blood. Drivers testing positive for this lower limit will receive a $200 fine and gain 50 demerit points.

The Science Media Centre covered this issue closely in 2010. You can listen to playback of a media briefing held at the time and access a relevant and free-to-use infographic on the SMC website.

The SMC collected the following expert commentary. Feel free to use these quotes in your reporting. If you would like to contact a New Zealand expert, please contact the SMC (04 499 5476; smc@sciencemediacentre.co.nz).

Dr Allan Stowell, Science leader, Alcohol Analysis Unit, ESR, comments:

“I do not believe the law will penalise “moderate social drinkers”.

“For example, a male of average build drinking two to three glasses of wine during a leisurely dinner, or three to four small bottles of beer during a social gathering lasting about two hours is highly unlikely to exceed 50 mg/100mL at the end of the drinking period.

“Women need to be a little more careful, but a woman of average build would be highly unlikely to exceed 50 mg/dL after consumption of two to three standard drinks, over a two hour period.”

Dr Eric Crampton, Senior Lecturer in Economics at the University of Canterbury, comments:

“Lowering the drink driving limit is likely to reduce accident rates. I have not yet had a chance to examine the review cited by Mr. Brownlee, but he suggests that reducing the limit from 80 to 50 milligrams will prevent accidents imposing social costs on the order of $20 million annually, or about $5 per capita per year. That will come at the cost of reduced alcohol consumption among those who enjoy more than a glass of wine with dinner or more than a pint over the course of an evening. Their reduced enjoyment should also count. I had previously estimated that drivers in the 50-80 range impose no more than about $4 in expected cost – the monetized value of the risk they impose – per trip.

“If those drivers judge their reduced enjoyment of the night out as costing more than $4, then the policy will have done harm even if it slightly reduces the road toll. I hope that the Ministry has accounted for these kinds of costs in their analysis.”