Prime Minister John Key says he wouldn't have more than one wine or two beers before getting behind the wheel of his car, but he is standing by the decision not to reduce the current blood alcohol limit until more research is done.

Transport Minister Steven Joyce last week announced a zero limit for recidivist and young drivers but said New Zealand-specific research over the next two years would look at the level of risk posed by drivers with a blood alcohol limit of between 0.05 and 0.08 (50mg-80mg).

During today's post-Cabinet press conference, Mr Key was asked if he would do a test to see how many drinks he could consume and remain under the legal limit, after a newspaper staffer was able to drink nine beers and still legally be able to drive.

"No, because I need to run the country the next day and I'd be messy after nine beers," he replied.

He said the limit was not a target but a maximum and people set their own limits using their judgment.

Variables including tiredness, food consumed and weight which were all different for individuals.

He said people should not assume they could drink nine beers and drive because that may not be true in their case. He limited himself to a single wine or two beers and did not think he would still be able to legally drive after nine.

Critics say there is overwhelming research already showing the value of reducing the level and also argue there is public support for the measure.

The Transport Ministry estimated reducing the level could save 33 lives, prevent up to 680 injuries, and save up to $238 million every year.

However, Mr Key said research out last week showed of 1045 drivers killed between 2004-09 only 10 had blood alcohol limits of between 0.05-1.0 who also had no drugs in their system.

"You can make a case that if you really wanting to lower the road toll a good place to focus is drugs and that is why the Government introduced measures to start testing people where police officers believed they had been taking drugs."