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[…] Under recently passed laws, police can now stop any driver, at any time, to screen with an oral swab for four illicit substances: THC (cannabis), cocaine, methamphetamine and MDMA (ecstasy).
[…] Drivers will face an initial roadside swab taking a few minutes; a positive result triggers a second test. If confirmed, the driver will face an immediate 12-hour driving ban and have their initial sample sent to a lab for evidential testing.
With nearly a third of all road deaths involving an impairing drug, moves like this are clearly aimed at a serious problem.
A bit misleading but never mind.
[…] The research on cannabis and driving impairment is mixed. Many studies show an associative rather than causal link: people who use cannabis more often tend to report more crashes, but not whether those crashes happened while they were impaired.
Unlike alcohol – where blood-alcohol concentration closely tracks impairment – no such relationship exists for THC. Cannabis is fat-soluble, so traces linger in the body and appear in saliva long after any intoxicating effect has passed, making saliva testing a relatively poor proxy for impairment.
For the other targeted drugs – the stimulants methamphetamine, cocaine and MDMA – the connection to driving impairment is also unclear. At lower doses, stimulants can even improve certain motor skills. The risks are instead tied to perceptual shifts or lapses in attention, which a saliva test cannot detect.
This is crucial. Take methamphetamine for example. We can all agree that someone driving strung out on meth is clear and present danger. But what about someone who has taken a threshold dose?
It’s also true that the connection to driving impairment remains unclear. For example there is at least one study showing that cannabis causes minimal driving impairment. There’s also at least one study showing the taking MDMA caused no driving impairment – it’s actually sleep deprivation that’s the problem.
[…] The policy’s focus on just four illicit drugs also raises questions of scope. In practice, these are among the easiest and most visible substances to target: the low-hanging fruit.
[…] Another pressing question is what happens when the test detects traces of cannabis long after impairment has passed. THC can remain detectable in regular users for up to 72 hours, even though its intoxicating effects last only a few.
That means a medicinal cannabis patient who took a prescribed dose the night before – or a habitual user with high baseline levels – could therefore test positive while driving safely.
In practice, some law-abiding drivers will inevitably be caught up in the process simply because of residual traces that pose no safety risk. Conversely, an inexperienced cannabis user may feel heavily impaired yet return a low reading.
This uncertainty reflects a deeper flaw in the system. When the previous government first designed the policy, it intended to test for impairment.
[…] Other jurisdictions have taken a different path. Many have returned to behavioural assessments of impairment – the traditional field-sobriety approach of observing coordination, balance and attention.
In the United States, for instance, officers often rely on such behavioural indicators because the law there still centres on proving a driver was impaired, not simply that they had used a substance.
Let’s be clear here. Random road testing is a gross invasion of our civil liberties. However, with regard to alcohol, as a society we decided that this is offset by the risk drunk drivers present.
But how much danger say do people who drive under the influence of cannabis present, and I’m talking overall here. Or even meth. Does it justify having people arrested merely because they have cannabis in their system?
And with alcohol we don’t just test for impairment we also test for level. In other words, if you’ve only had half a glass of beer you’re fine.
Given that it’s so obvious that it’s much better to test for impairment than presence, I can’t help but think that all this is more about politics rather than road safety, i.e., it’s aimed at rah-rah voters who want the government to be ‘tough’ on crime and tough on druggies etc. Funny thing is these same people quickly change their tune when it’s their son or daughter before court with their future career in the balance because they had a small joint the night before.
