Today’s launch of roadside drug-testing marks one of the biggest changes in road policing since 1993, which saw the introduction of both compulsory breath-testing and speed cameras.

Drivers in the Wellington Police District can now be required to undergo a roadside drug test. The testing regime is expected to be rolled out to the rest of the country in 2026.

To be tested, drivers will have to wipe the drug screening device’s pads on their tongue and then wait about 10 minutes for a result.

The roadside test screens for recent use of THC (cannabis), MDMA (ecstasy), cocaine and methamphetamine. If nothing is detected, the driver will be free to go. But if the test returns a positive result for any of these substances, two things will happen.

The driver will have to provide a saliva sample for lab testing and take a second roadside test. If the second roadside test is also positive, the driver will be banned from driving for 12 hours. If it is negative, the driver will be free to go, however their saliva sample will still be sent to the lab for additional testing.

While the roadside test only screens for four drugs, the laboratory testing will test for all 25 drugs that can result in a drug-driving offence. Each drug has a different threshold for the amount of the drug that is allowed to be present in a driver’s saliva.

The thresholds are set to indicate the recent use of drugs, as opposed to historical use or accidental exposure.

If any of these drugs exceeds the threshold, an infringement notice will be issued to the driver.

Police Minister Mark Mitchell said: “Roadside drug testing is another step to keep the public safe by giving Police the tools they need to better detect and deter drug-impaired drivers.

“Testing drivers will help reduce the deaths and serious injuries caused by drug driving. The message is simple – if you’ve taken impairing drugs, then don’t drive, or expect to be caught and face consequences for your actions.”

Superintendent Steve Greally, director of road policing, said if an infringement was issued after laboratory testing, drivers would have the ability to apply for a medical defence if it was for a drug that had been prescribed to them.

“Drivers cannot use a prescription or medical note at the roadside to stop them from undergoing a test or to dispute a positive saliva screening test result.

“Those who refuse or fail to comply with a roadside drug screening test will be issued with an infringement notice that includes a $400 fine, 75 licence demerit points, as well as being forbidden to drive for 12 hours.”

Chris Knox is a scientist turned data-journalist who investigates the stories behind the numbers, and creates interactives for Herald readers to explore them.