IT鈥橲 official: smoking dope makes you a worse driver. But cannabis has less
effect on driving ability than alcohol, according to a study by the Transport
Research Laboratory (TRL) in Crowthorne, Berkshire.
The Department of Environment, Transport and the Regions asked the TRL Safety
Department to investigate the effect of cannabis intoxication on driving
ability. Cannabis is by far the most common illegal drug found in the
bloodstream of road accident victims, and THC鈥攖he active ingredient in
cannabis鈥攃an remain in the body for more than a month.
Barry Sexton and his colleagues at the TRL recruited 15 volunteers to
complete driving tests while under the influence of low or high doses of
cannabis, or no drug at all. The volunteers either smoked ready-rolled cannabis
joints or rolled their own with resin supplied under government licence. They
were then put through their paces on a sophisticated driving simulator.
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The researchers measured their accuracy at steering the car, known as
鈥渢racking ability鈥�, and other psychomotor responses, such as hazard perception
and braking responses. They took blood and saliva samples at regular intervals
and also tested the subjects鈥� coordination, balance and timing.
The first thing the researchers noticed was that the subjects drove more
slowly under the influence of dope, compensating for their intoxication by
driving more cautiously. Tracking ability was the only test criterion that was
adversely affected: the volunteers found it very difficult to follow a
figure-of-eight loop of road when given a high dose. Reaction times to motorway
hazards and performance on cognitive tests in the lab were not significantly
affected.
Trials previously completed under similar test conditions at the TRL have
shown that alcohol and tiredness have a more adverse effect on driving ability,
affecting higher cognitive processes. The results of the cannabis and driving
study agree with similar research carried out in Australia, the US and
Holland.
Pete Henshall of the Legalise Cannabis Alliance, which is a British political
party, comments that 鈥渁ny person who is not in full control of their body should
not drive, be it through tiredness, alcohol, cannabis or drugs鈥ut everything
must be seen in proportion. We need to legalise and regulate cannabis in a
similar way to alcohol to be able to see the size of the problem.鈥�
Jane Eason of the Royal Society for the Prevention of Accidents favours the
roadside tests to spot cannabis intoxication now being tried by British police.
鈥淲e would welcome any measure that might make the roads of Britain safer.鈥�