Drivers took to the skidpan after smoking light and heavy doses of cannabis. Picture: DENIS DROPPA
Drivers took to the skidpan after smoking light and heavy doses of cannabis. Picture: DENIS DROPPA

Dagga may be used in the privacy of your home, but may it be used in the privacy of your car? And does being high make you a worse driver?

After the Constitutional Court’s momentous September 18 ruling effectively decriminalised the private use of cannabis in SA, it raised the prospect of more people driving under the influence of the drug. Would the ruling affect road safety as newly-emboldened dagga users came “out of the closet” and drive around stoned?

To try to answer the question, pro-cannabis lobbyists Fields of Green for All set out to determine the effects of driving under the influence of cannabis.

They set up a driving experiment at a closed test facility in which volunteers drove under the influence of cannabis.

The volunteers were a mix of regular cannabis users, semi-regular users and first-timers. Motor News, along with Ignition TV, was also invited to witness the  “Driving High” experiment which was run at the Gerotek test centre by professional driving instructor Grant McCleery of Yokohama Driving Dynamics.

The test took the form of a gymkhana in which the volunteers had to drive a car through a series of cones on a wet and slippery skidpan. They first drove the course sober, then again after smoking a small amount of marijuana, and finally a third time after smoking another, heavier dose.

The driving test took the form of a skidpan gymkhana and participants were rated on their technical skills and reaction times. Picture: DENIS DROPPA
The driving test took the form of a skidpan gymkhana and participants were rated on their technical skills and reaction times. Picture: DENIS DROPPA

Each of the three runs were timed to see how quickly the drivers were able to complete the slippery and technical circuit, and time penalties were added for each cone that was knocked over.

Of the 12 volunteers who drove, some completed the course slower under the influence of cannabis, and some got faster. Of those whose driving improved, it may have been due to participants getting more familiar with the course due to repetition, said McCleery.

However, in the third run the results were more conclusive. Where the volunteers were more heavily under the influence of cannabis, five of the drivers knocked over cones, while in the first two runs, only one driver had done so.

When interviewed, most of the regular cannabis users in the driving test acknowledged that while they didn’t feel their driving was impaired while on a mild high, it deteriorated while they were very high, and that they wouldn’t normally drive when in such a condition.

“My driving does become impaired when I’m very high, but I realise it and I don’t drive - unlike drunk drivers who think they drive better when they’ve had alcohol,” commented one participant.

A US study on the effects of medical marijuana on driving by the University of Colorado, Montana State University, and the University of Oregon found that “drunk drivers take more risk, they tend to go faster. They don’t realise how impaired they are. People who are under the influence of marijuana drive slower, they don’t take as many risks.”

Another volunteer in last week’s “Driving High” experiment, a regular cannabis user, remarked that he regularly drives after taking a mild dose of marijuana as it calms him down and reduces road rage.

One of the volunteers from the Fields of Green for All organisation who participated in the Driving High test. Picture: DENIS DROPPA
One of the volunteers from the Fields of Green for All organisation who participated in the Driving High test. Picture: DENIS DROPPA

Authorities take a dim view of anyone driving under any mind-altering substance however and, as with alcohol, the law doesn’t allow cannabis users to decide for themselves whether they feel fine to drive.

Section 65 of the National Road Traffic Act states: “No person may drive a vehicle or occupy the driver’s seat of a motor vehicle of which the engine is running on a public road while under the influence of intoxicating liquor or drug having narcotic effect.”

Proving whether a person is under a narcotic effect is the difficult part, however.

As tetrahydrocannabinol (THC), the psychoactive constituent of marijuana, remains in a person’s system for much longer than alcohol - sometimes for weeks - it’s tricky to establish limits and laws around cannabis use.

“In theory‚ any person caught with even traces of marijuana in their system whilst driving can currently be arrested and/or prosecuted. But because it can remain in a person’s bloodstream for hours to days after use‚ a person who tests positive for marijuana isn’t necessarily intoxicated,” said Rhys Evans‚ director at ALCO-Safe‚ which supplies drug and alcohol testing equipment in SA‚ in a statement

“At present‚ no limit has been established to determine how much THC needs to be present in the bloodstream for a person to be considered intoxicated‚” said Evans.

He said the likelihood of a driver being tested for drugs at a roadblock were minimal due to a lack of testing equipment available to traffic officers.

“As a result‚ drivers that indulge in substances such as marijuana are less concerned with being caught in a roadblock than if they have consumed alcohol‚” Evans added.

“The state has a lot of work to do now in order to control the use of driving under the influence of THC. They will have to implement an acceptable limit in either blood, urine or saliva.”

Wayne Minnaar, spokesperson for the Johannesburg Metropolitan Police Department, admits that motorists arrested for drunk driving far outnumber those arrested for driving under the influence of drugs. As there’s no breathalyser for drug testing, traffic officers can only visually determine if they believe a driver is under a narcotic effect and arrest them if necessary, he says.

A number of overseas tests have shown some increased road-safety risk associated with cannabis use by drivers, but have also identified other legal medications as producing similar or increased impairments to driving, including antianxiety medications, penicillin, antiasthmatics, and sleep medicine.

  •  The “Driving High” test will be aired on Ignition TV from October 27.