Think you're good at judging your own sobriety before you drive? Think again.

According to the findings of a University of Waikato study, drivers are extremely poor judges of their own sobriety.

The study was produced by the university's Traffic and Road Safety (Tars) Research Group for the Government to assist in the decision to lower the legal limit for New Zealand drivers.

The legal blood alcohol limit is due to drop from 80 milligrams per litre of blood to 50 milligrams next year.


In the study, conducted by Associate Professor Samuel Charlton and Dr Nicola Starkey from the university's School of Psychology, participants consumed drinks of varying alcohol quantities while their driving skills were tested in a simulator.

The participants were not told how much alcohol was in their drinks.

"In general, alcohol affects many areas of cognitive performance, including the ability to judge how sober you are," said Dr Charlton.

"After a while, the participants felt like they had 'sobered up' enough to drive, even though they had as much alcohol in their blood as before. The really dangerous thing is that although they felt better, their driving and cognitive performance was significantly worse than before."

Dr Charlton said the study found that driving performance actually gets worse over a period of time, even though the amount of alcohol in the bloodstream stays the same.

Last month Transport Minister Gerry Brownlee introduced the Land Transport Amendment Bill 2013, legislation that will lower the adult drink-driving limits.