‘Roadside drug testing’s puritanical political agenda’

The Government has announced the rollout of roadside drug testing for four illicit substances – THC (cannabis), MDMA (ecstasy), methylamphetamine (meth), and cocaine – after an amendment to the Land Transport Act. But just because these drugs are illicit does not mean they always impair driving ability, which makes me question the intent of the scheme and whether public safety is really the priority being exercised here.

Police will be able to take an oral sample, and a testing kit will flag potential drug presence, which will be confirmed (or not) by proper laboratory analysis. Drivers with a positive result will not be allowed to drive for 12 hours, and a positive lab result means an infringement notice. Refusal to take the test carries the same penalties as a positive result.

The dangers of driving “impaired” by substances including alcohol, opioids, and other medications are well documented. As stated in the Government’s press release: “Around 30 percent of all road deaths now involve an impairing drug. If you take drugs and drive, you’re putting innocent lives at risk – and we will not tolerate it.”

Many drugs can reduce reaction times, fine motor skills, or critical thinking and judgment. Drunk driving is a leading cause of road-based injury, and both licit and illicit drugs are increasingly implicated as causes or contributing factors in road accidents.

At first glance this announcement may seem like a no-brainer, but the specifics of this scheme raises the question of what is really behind this plan. Is this a genuine effort to improve road safety by “cracking down” on “drug drivers”, or is this an attempt to police drug use under the guise of road safety?

Driving impaired is clearly a problem for road safety, but this scheme does not test for impairment. Rather, it tests for (historical) use of drugs. Although those can be the same thing, often the link between drug use and driving impairment is much more complex than these roadside devices can know.

Take cannabis, for which the criminal blood limit has been set at 3ng/ml of THC. For occasional users such a level can be detected for about 24 hours after consumption; for frequent users this can be over 72 hours (three days). If you smoke on a Sunday afternoon, you could be over the legal limit until Thursday morning. Cocaine is similarly detectable by these kits for about 12 hours, even though the effects of the drug hardly last an hour.

The Attorney-General’s report on the legislative amendment states: “The Ministry of Transport and Police consider that there is likely to be a high number of drug-impaired drivers who are not captured under the [current Compulsory Impairment Test which includes the hop-on-one-leg test] regime because there may be no observable signs of impairment at the time of driving.”

If the impairment is not observable, there are no deficits of coordination, speech, or motor skills detected by specially trained police, then what does it mean to be impaired?

The impact that different drugs have on driving ability remains contested, and effects are determined by far more than the concentration of these substances in blood or saliva.

Across the ditch in Victoria, all drivers hospitalised after a car crash have blood tests for meth, MDMA, alcohol and THC, unlike in New Zealand, where many are only tested for alcohol.

A study on injured drivers in Victoria investigated whether the presence of drugs changed the odds ratios (OR) of the injured driver being at fault. With a baseline of one, alcohol increased the OR to 16 (and to 73 at high levels), while meth had an OR of 19. Cannabis did have a small effect, with an OR of 1.9, but this is lower than the OR of drivers over 60 (1.94) or 18 to 25 (2.51).

Very few instances of vehicle accidents in New Zealand involve cocaine. Yes, it’s short acting, but it’s also a stimulant, a class of drugs that can improve reaction times and motor skills.

Stimulants may lead to more aggressive or careless driving, but they also can improve driving in laboratory and real-world conditions. Military pilots and soldiers have often been given amphetamines to help them focus and to carry out long missions, and drivers with ADHD (who are more likely to be involved in accidents), generally have better road outcomes on stimulants (although at lower doses than recreational users).

The choice of kits further illustrates the political agenda behind this scheme. There are 25 drugs that an independent panel has assessed as being of highest concern, including eight opioids and 10 sedatives (mostly benzodiazepines). None of these substances will be detected at the roadside, despite each impairing more drivers than cocaine and MDMA combined.

The inclusion of a medical defence similarly points to an unspoken politics: why is driving impaired permissible if caused by legally prescribed drug? Surely road safety is about impairment, regardless of what drugs a driver is using. Looking into the criminal limits reveals similar inconsistencies: tramadol is set at 250ng/ml when its therapeutic effects are felt at around 100ng/ml.

It is not just the science of this scheme that is questionable, with the law society, Attorney-General, and others raising concern at the unreasonableness of the powers given to police to stop, search, seize, and detain ordinary citizens without any cause. The inaccuracy of these devices should also scare you; the legislation had to be amended again because no testing device met the 2022 standards. These kits can give false positives 10 percent of the time.

Ultimately this feels like a poor, puritanical attempt at policing drugs, which needs a different conversation entirely. If the Government is serious about upholding road safety, then drug impairment needs to be assessed, not the use of illicit drugs.