Next month, Wellington will be the first place to introduce police use of a saliva test on drivers, with plans for the rest of the country to adopt it by mid-2026.
Using new oral-fluid testing devices, police will be allowed to stop any motor vehicle and test the driver for four specific drugs, including THC (cannabis), methamphetamine (meth), MDMA (ecstasy), and cocaine.
An Australian expert, however, describes it as a scattergun method that does not consistently detect impairment.
Dr Michael White, an adjunct senior fellow at the University of Adelaide’s School of Psychology who has studied cannabis-related road accidents, said that while the tests identified the presence of drugs, they did not consistently measure impairment.
He explained that the issue was not only the duration of the detection window but also the number of people who are genuinely impaired after using drugs such as cannabis.
“There’s a lot of research that says regular cannabis users are not impaired even if immediately after taking it, so that produces a sort of questions of justice,” White said.
“It is a scattergun approach, many people who are regular users won’t be impaired even if they test positive.”
The New Zealand government said impairing drugs are involved in 30% of all road deaths and that increased screening will enhance road safety.
“We know that they’re [drugs] a major factor in many road deaths and serious injuries,” Transport Minister Chris Bishop previously said.
“We’re now making sure that police are equipped with roadside oral fluid screening as a road safety tool to enable the enforcement.”
Dr White highlighted that there is no strong evidence showing that roadside testing has effectively reduced drug-impaired driving or accidents.
“Australia has been quite negligent on actually trying to evaluate roadside drug testing.”
“They’ve got a very passive approach, they simply say RBT (random breath testing) for alcohol has been successful, RDT (roadside drug testing) for drugs looks a bit like random breath testing, and therefore it ought to be successful. There’s never been any evaluation in Australia that clearly shows that roadside drug testing actually works.”
Based on previous reports, the Australian company Pathtech Pty Ltd will provide the Securetec DrugWipe 3S devices along with oral fluid collection kits for taking samples that will be sent to a laboratory for analysis.
Dr White explained that drugs and alcohol affect drivers differently, and testing should be designed according to the level of crash risk.
“I think policy should be based on crash risk, the crash risk from cannabis is relatively low; it’s less than for a BAC of 0.5. So cannabis might increase your risk of crashing by up to 50%, alcohol at a BAC of 0.5 doubles your risk, so it increases it by 100%.”
Dr White noted that methamphetamine presents a challenge because it may not directly impair a person but can instead increase aggression and thrill-seeking behaviour.
Another major concern he raised about the testing was its handling of legal drugs like benzodiazepines and opioids, which he said can also lead to fatal car accidents.
“Some Australian research has said that benzodiazepines account for twice as many road crash fatalities as cannabis, and opioids account for twice as many; now both of those are legal drugs.”
“So that’s one thing that neither Australia nor New Zealand really takes into account: the damage done by legal drugs.”
Pharmacist and AUT senior lecturer in Biosciences Dr Catherine Crofts had also expressed concerns about the limited information regarding how the new testing might affect people with prescriptions such as dexamphetamine.
According to Dr Crofts, about 50% of Kiwis with ADHD are taking dexamphetamine or lisdexamfetamine.
“We know that some of the tests that are out there in the community do cause some cross-reactivity, and I’ve just found that there are some that don’t,” she said.
“But we haven’t seen anything about what the police are going to do or how it is going to be managed when somebody who cross-reacts is legally on these medicines.”
Dr White mentioned that for detecting subtle levels of impairment, some have proposed using phone applications to evaluate people’s reaction times, although he remains sceptical about the effectiveness of these apps.
“I’m not convinced that those apps are particularly good, but at least they’re trying to measure impairment, which is a step in the right direction rather than measuring presence.”