NO PROOF CANNABIS PUT DRIVERS AT RISK

Studies had found it impossible to prove cannabis adversely affected driving, an Adelaide University researcher said yesterday.

Professor Jack Maclean, director of the road accident research unit, said, while there was no doubt alcohol affected driving adversely, that was not the case with marijuana.

"It has been impossible to prove marijuana affects driving adversely," he told the Australian Driver Fatigue Conference in Sydney.

"There is no doubt marijuana affects performance but it may be it affects it in a favourable way by reducing risk-taking."

Professor Maclean said a study of blood samples taken by SA hospitals from people injured in road accidents found marijuana was the second most common drug, after alcohol, in the bloodstream.

Those with marijuana in their blood, however, were at fault in less than half of the accidents.

"Alcohol was by far the most common drug and 80 per cent of those with alcohol on board were judged to be responsible (for accidents)," he said.

"The next most common drug, but much less, was marijuana and about 48 per cent of the people with marijuana were judged to have been responsible for their crash."

He said the lack of proof that marijuana was detrimental to driving was not because of a lack of effort by researchers.

"I can say that there are some quite distinguished researchers who are going through incredible contortions to try and prove that marijuana has to be a problem," he said.

Professor Maclean said some researchers also found the risk of crashing while driving at the speed limit in a metropolitan area actually decreased if a driver had been drinking but was under the 0.05 blood alcohol limit.

"Perhaps for some people one or two glasses of alcohol may steady them down," he said.

As speed and alcohol concentration rose, however, the risk of accidents rose exponentially.