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Searching for a missing linkIt is common knowledge that cannabis affects people’s judgement, but researchers are now looking into how this widely used drug impairs driving performance. ALLISON HARDING reports The tragic link between alcohol and road accidents is well established, but Monash scientists are now leading the way in investigating the effect of cannabis use on driving ability. Researchers from Monash's Centre for Applied Drug and Alcohol Research are working with the Monash University Accident Research Centre (MUARC) and Turning Point Alcohol and Drug Centre on a major project to establish the impairment cannabis causes to young drivers.
While laws currently exist in Australia prohibiting driving under the influence of various drugs (including some prescription drugs), charges can sometimes be difficult to prove in court because of problems in establishing the level of a driver’s impairment. Project leader and centre co-director Associate Professor Jenny Redman says the effect of cannabis on driving ability needs to be confirmed before any test can be developed. "It’s critical to know how the drug impairs and how realistic it is to get some sort of measure of impairment. You have to have a test that consistently stands up in court, so police can prove that a particular level of cannabis caused the impairment," she says. "With alcohol it’s a bit different – they’ve set the level and anything over .05 is illegal, regardless of the level of impairment." But increasingly, both in Australia and internationally, there are cases of drivers being picked up for poly drug use, Dr Redman says.
"For a long time MUARC has been interested in young drivers and how they differ from more experienced drivers," Dr Redman says. "And one of the things that comes out is that although they’re skilled in certain ways, such as their very quick reaction times, when they’re put under pressure – if they have to concentrate on another task while driving or something unexpected happens – they don’t cope as well. This makes sense given their level of learning and experience." Dr Redman says research reveals that younger drivers are the ones who most often use cannibas and drive. A high percentage – about 80 per cent – of drivers picked up with cannabis in their system also have alcohol in their blood. "That common combination was the obvious one to look at, and we decided to compare that young group with a group of older, more experienced drivers (aged between 25 and 40 years)," she says. The cannabis cigarettes used in the study are imported under strict regulations from the National Institute on Drug Abuse in the US, as researchers have to know the exact level of the drug being given in the experiments. Dr Redman and her team are testing 60 drivers – two groups of 30 – who have smoked and drunk various levels of cannabis and alcohol. They then get behind the wheel of MUARC’s state-of-the-art driving simulator. "All the subjects ‘drive’ in all conditions, so there are two levels of alcohol and there are two levels of cannabis and then all the combinations," Dr Redman says. "We’re testing eye movements and balance as well as driving skills – not only keeping constant speed and staying on the right side of the road, but also coping with unexpected events and problems on the road to see how people react. "Participants then do a few other behavioural tests and we take blood samples from them. We know exactly how much they’ve smoked because the content of the cigarettes is strictly regulated, as well as how much they’ve drunk, so we can equate their blood level with any impairment." The alcohol levels given to the subjects are not excessive. Otherwise, Dr Redman explains, the alcohol would wipe out the whole effect of the cannabis. MUARC research fellow Dr Michael Lenne says one of the key features setting this study apart from similar overseas investigations is that driving ability will be measured across a comprehensive range of real-life situations through the simulator. "Driving performance is measured across rural, residential, arterial, and freeway conditions. Some of these drives also contain additional (secondary) tasks that place a further workload on the driver," he says. "Another key feature of the study is the inclusion of risk perception drives which contain specific high-risk situations such as swerving to avoid a pedestrian and deciding when to turn across oncoming traffic. "Inclusion of these risk perception drives, along with the four other conditions that will be used, will allow for a thorough examination of the effects of cannabis on driving skills." Much of the related research, both in Australia and overseas, is aimed at developing and evaluating a saliva-based device that can screen for drugs such as cannabis at the roadside, Dr Lenne says. "While the roadside screening devices will be able to detect the presence of a drug, our current cannabis simulator study will provide valuable information about the link between cannabis in the body and the magnitude of the impairment caused by the use of cannabis." Dr Redman believes the study will reveal that cannabis causes some impairment – and that the combination of cannabis and alcohol is particularly dangerous for younger inexperienced drivers when they’re challenged or have a secondary task on the road – such as negotiating roadworks or traffic jams. She says that while there have been ethical issues in importing drugs and using them in the experiments, Monash has been supportive of what she believes is an important research project. "You cannot advise politicians on what laws should be made if you can’t give them scientifically obtained evidence," she says. ACTION: For more information about the research project, contact Dr Jenny Redman on +61 3 9905 3957 or email jenny.r.redman@sci.monash.edu.au. For more information about MUARC, contact +61 3 9905 4371 or visit www.general.monash.edu.au/MUARC/ |
The study is jointly funded by the National Health and Medical
Research Council and VicRoads, and other baseline MUARC sponsors (the
RACV, the TAC and the Department of Justice).
Young drivers between 18 and 21 are the main targets of the centre’s
research project, which is expected to take about 18 months.