Worldwide, policy makers have many questions about the use of cannabis in traffic. Although cannabis seems to have an influence on driving ability, there are many individual differences in how a person reacts. Reason for the ICADTS to set up a working group of experts. The working group was co-chaired by UM, Traffic Injury Research Foundation Canada (TIRF) and Swinburne University in Australia.

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Alcohol and drugs

Whereas for alcohol it is clear where the line for safe driving lies, this is not entirely clear for cannabis. "Unlike alcohol, research into the harmful effects of THC - the active ingredient in cannabis - on driving is much more complex, because with cannabis there is no clear relationship between quantity and its effect," says Jan Ramaekers, a researcher at UM and former president of the ICADTS.

His colleague Robyn Robertson, co-chair and CEO of TIRF, explains: "In alcohol, a blood alcohol concentration (BAC) accurately reflects the amount of alcohol consumed. Despite variations between subjects, research shows that as the BAC increases, so does the degree of rice impairment. However, THC concentrations do not accurately reflect the amount of cannabis consumed or the degree of impaired driving of individual drivers, so determining the degree of impairment is much more complex and less straightforward."

Uniformity in policy

Despite individual variations in response to cannabis, researchers agree that cannabis can influence driving behavior. In combination with alcohol, even when used in low doses, it is a hazard to get into a car. Policy in this area is badly needed. In the Netherlands the sale of cannabis is formally punishable, but has been tolerated for decades under certain conditions. Recently, a number of countries have legalized recreational and/or medical cannabis use, including Canada, Georgia, Malta, Mexico, South Africa and Uruguay. In over a third of U.S. states, cannabis is legal. Other jurisdictions, such as Germany, are considering such a move, and this global trend is likely to continue. This also increases the need for a coordinated approach to cannabis use in traffic.

To date, jurisdictions have taken a variety of legal approaches to address the problem of drunk driving. "A priority for the future is to establish greater uniformity in how impaired driving is determined and how the results are recorded. This would allow us to pool data from different jurisdictions and better assess the impact of expanding legalization on road safety," says Tom Arkell, Research Fellow at Swinburne University of Technology.

More information on the website of the ICADTS.