Preventing cannabis users from driving under the influence of cannabis

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Release date: Tuesday 25 October 2005

A survey of 320 recent cannabis users in Sydney and Newcastle has shown that 78 per cent have driven at least once in the past 12 months within one hour of using the drug. Twenty-seven per cent reported driving under the influence of cannabis at least once a week.

The NSW Bureau of Crime Statistics and Research (BOCSAR) and the National Drug and Alcohol Research Centre (NDARC) conducted the survey as part of an investigation into ways in which cannabis users might be deterred or persuaded not to drive a motor vehicle while under the influence of cannabis.

Although the study found no direct link between cannabis use and accident risk, more than a quarter of those interviewed believed that cannabis intoxication impaired their driving ability.

To assess the potential effectiveness of tougher penalties and random drug testing, cannabis users in the study were presented with various scenarios and asked whether they would drive under the influence of cannabis in that scenario.

Drivers were randomly assigned to one of four groups, based on whether the scenario indicated that roadside drug testing was in operation and how harsh the fines and licence disqualification periods would be if they were caught.

The threat of tougher penalties exerted no effect on the stated willingness of cannabis users to drive under the influence of cannabis. The threat of random roadside drug testing, however, exerted a strong deterrent effect.

By contrast, it was found that merely providing users with information about the dangers of driving under the influence of cannabis would have little effect on deterring this behaviour.

Commenting on the findings, the Director of the Bureau, Dr Don Weatherburn, said that the failure in the current study to find any direct relationship between cannabis use and accident risk should be treated with caution as the number of cannabis users interviewed was relatively small. Other studies with larger samples have shown evidence of a direct effect.

"Small increases in the risk of a road accident can have catastrophic outcomes for individual families", he said.

"There is enough evidence around to justify determined efforts to reduce the rate at which people drive under the influence of cannabis, whether alone or in conjunction with alcohol or other drugs".

"It is clear from the current study that measures which increase the risk of detection for drug driving are likely to be far more effective than simply increasing the penalties for drug driving. If we are to achieve this objective, though, we are going to need a fast, cost-effective and accurate means of gauging a driver's level of cannabis intoxication".

Further enquiries: Dr Don Weatherburn: 02 92319190 (work), 0419-494-408 (mobile)