Minister's night out would be shorter if law changed

When Transport Minister Steven Joyce confidently proclaimed he could drink three-quarters of a bottle of wine in 90 minutes and remain under the 80 milligram blood-alcohol limit, he was probably right.

But that will change dramatically if a proposed 50mg of alcohol per 100ml of blood is introduced.

A 750ml bottle of wine holds about eight standard drinks, meaning Mr Joyce would consume roughly six standard drinks before getting behind the wheel - well inside current guidelines that allow an average-sized man anything up to 6.9 standard drinks in his first hour - almost seven 330ml cans of 4 per cent beer.

However, under a 50mg blood limit that maximum would plummet to no more than 4.7 standard drinks an hour, which could spell an early night for the minister.

And it's unlikely he would be able to surrender the car keys to Mrs Joyce.

Lowering the blood-alcohol limit to 50mg would drop the number of standard drinks for an average-sized women from a maximum 4.6 an hour to 3.1.

The law change would reduce the limit of 400 micrograms of alcohol per litre of breath to 250 for drivers aged over 20.

At the time, Mr Joyce was quick to point out he had never actually put such drinking to the test, using the point to show how "ridiculous" the current alcohol limits were.

Yesterday, Capital & Coast DHB chief medical officer Geoff Robinson described New Zealand's blood-alcohol limit as "relatively high" by international standards.

A blood-alcohol reading of 79 was "a legal sanction" to drive drunk and evidence suggested impairment became "obvious" beyond 50mg of alcohol per 100ml of blood.

"It's quite a lot of alcohol required to reach 80."