New study into alcohol and driving produces surprising results

Associate Professor Samuel Charlton, from the University of Waikato’s School of Psychology, recently completed a large research project showing that drivers are extremely poor judges of their own sobriety and that the same amount of alcohol in the blood can have different effects depending on how long it’s been since you started drinking.

Drinking study

In the study conducted by Dr Charlton and Dr Nicola Starkey, also from the School of Psychology, participants consumed drinks of varying alcohol quantities while their driving skills were tested in a simulator. 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.”

Driving performance

The finding that driving performance actually gets worse over a period of time, even though the amount of alcohol in the bloodstream stays the same, is called acute protracted error.

Although acute protracted error has been reported previously with high levels of alcohol, the research by Drs Charlton and Starkey shows that it can happen even with moderate amounts of alcohol, such as a blood alcohol concentration (BAC) of 0.05, the new legal limit for New Zealand drivers as of 2014.

Government decision-making

The research project was produced for the government to assist in the decision to lower the legal limit for New Zealand drivers from the current level of 0.08 BAC to 0.05 BAC.

The project follows on from a series of studies conducted by Dr Charlton and his colleagues at TARS, including self-explaining roads and driver awareness, the use of cell-phones while driving, and a nationwide novice driver training and education programme.

TARS is an independent provider of research based in the University of Waikato’s Faculty of Arts and Social Sciences. Their research has contributed to the improvement in the safety of drivers and roads in New Zealand and internationally. TARS has state of the art research facilities, including the most advanced driving simulator laboratory in New Zealand.

The University of Waikato