Drug-impaired drivers cause more fatal crashes than drink-drivers, a new study has found.

The Automobile Association (AA) study found that 79 drivers involved in fatal crashes last year tested positive for drugs, compared to 70 who were above the legal alcohol limit or refused to be tested.

It represents is a huge swing from the 14 crashes in 2013 that involved drug-impaired drivers, compared with 53 who were intoxicated or avoided tests.

The 2017 findings are thought to be the first time that drugs have overtaken alcohol in the statistic. Some drivers will have tested positive for both drugs and alcohol.

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The study included drivers who had taken prescription medications above recommended levels, or drugs known to impair driving.

The two most commonly detected drugs, excluding alcohol, were cannabis and methamphetamine.

A particularly worrying trend is that the cases of P being detected has shot up in recent years.

AA road safety spokesman Dylan Thomsen said the figures showed drug-driving was an increasing problem in New Zealand.

He believed police should be given the power to carry out roadside saliva-based drug tests.

"We now have more crash deaths where people test positive for a drug than alcohol – it's time to act," he said.

"We have to give police saliva-based testing devices to catch impaired drivers.

"No one wants someone who is high, driving towards their family at 100km/h but right now the chances of being caught drugged-driving is tiny. We have to change that."

The Land Transport Act states it is an offence to drive while impaired and with evidence in the bloodstream of a qualifying drug.

Last year 79 drivers who were involved in fatal crashes tested positive for drugs. Photo / Michael Craig
Last year 79 drivers who were involved in fatal crashes tested positive for drugs. Photo / Michael Craig

The presence of a qualifying drug alone is not enough for an offence; there must first be impairment as demonstrated by the compulsory impairment test, which looks at the driver's eyes and tests that they can walk and turn and stand on one leg.

Thomsen said the test takes a huge amount of an officer's time.

"The saliva-testing devices being used in many other countries would be much faster and allow many more potentially drug-impaired drivers to be tested than the current approach," Thomsen said.

Although the saliva tests would initially only detect common illicit drugs (like cannabis, P and Ecstasy), the AA believes it is better to test for some impairing substances rather than none.

Because the testing devices use saliva they are designed to catch people who have used drugs within a few hours of getting behind the wheel.

Associate Transport Minister Julie Anne Genter said she had asked officials to look at the problem and what other enforcement tactics could be used.

But she was unsure whether saliva-based tests were the best option.

"Solutions to tackle drug-driving need to be based on evidence and ultimately be effective.

"I am aware that there remains a number of practical challenges around saliva testing, including the reliability of the testing technology and the time it takes for police to obtain an accurate result," she said.

"I've asked officials to take another look at the drug-driving problem as part of a new road-safety strategy and action plan. This will consider the potential for additional enforcement options.

"Police already have the power to require a driver, who they suspect has used drugs, to undergo a compulsory impairment test and follow-up blood test. If a driver fails these tests they can face criminal sanctions."

The AA accepts opponents of roadside drug testing have concerns about the accuracy and speed of the devices but these can be answered by using them in a targeted way and having confirmation tests to double-check results.

"Drug testing does cost more than alcohol testing but the Ministry of Transport has estimated that every dollar spent would deliver $8 in savings from having fewer crashes on our roads," Thomsen said.

"Drug testing of drivers is working in Australia, the UK, France, the Netherlands, Norway, Denmark and Ireland and it can work here."

Brake, the road safety charity, supports the AA's calls for roadside drug-screening devices to be used by police.

Director Caroline Perry said the figures were extremely concerning.

"We know drug-driving is a significant problem; this data further shows the extent of the issue and that we need to do much more to address it.

"We want to see an increase in enforcement and the use of roadside drug-screening devices, to catch drugged drivers and deter people from drug-driving," she said.

"Drugs affect your coordination and reactions, seriously affecting your ability to drive. We urge people to never mix drugs and driving, it can easily be a lethal combination."

National MP Jami-Lee Ross has a member's bill before Parliament that would allow for roadside saliva testing for meth, Ecstasy and cannabis.