Critics have pointed out the government's plan to triple roadside drug testing to 97,000 annual test by 2017 meant drivers need only test positive to any trace of cannabis in their system to be convicted and have their licence disqualified for a minimum of six months, irrespective of whether they are intoxicated. Documents obtained by The West Australian have called drug-driving test results into question. Credit:Rohan Thomson Greg Barns, barrister and spokesman for the Australian Lawyers Alliance, said the "government had a clear obligation to provide accurate and scientifically robust information about how to comply with the laws." "To simply say do not use drugs is absurd and ignores reality." The official advice on detection levels from the NSW government is limited to a single line on the Centre for Road Safety website: "Cannabis can typically be detected in saliva by a mobile drug testing test stick for up to 12 hours after use."

Minister for Roads Duncan Gay said the zero-tolerance approach was motivated by deterrence, after drug driving was linked to 14 per cent of road fatalities in 2014. "My advice is don't take illegal drugs and if you do, be responsible and conservative with your decision of when it is safe to drive to avoid the consequences." Last week Magistrate David Heilpern in Lismore Local Court found 33-year-old Joseph Carrall tested positive for THC - the main psychoactive in cannabis - nine days after smoking it. The case highlighted the abounding confusion around the state's drug-driving testing regime, with Magistrate Heilpern acquitting Mr Carrall on the grounds he had reasonably relied upon a police officer's advice that he must wait one week after smoking cannabis before driving. Magistrate Heilpern was scalding in his assessment, describing the dearth of information around detection levels as part of the "mystery and uncertain-by-design of the current testing regime".

While he returned one of four not guilty verdicts in thousands of drug-driving matters in the past year, he is not the first to publish a finding at odds with the government's 12-hour window. Judge Richard Cogswell, hearing an appeal in the District Court in Bega in August last year, found Klaus Halper guilty after testing positive. However Judge Cogswell accepted evidence that Halper smoked the cannabis four days before the test, and that he used the cannabis instead of a "strong regime of prescription pain killers" following a serious car accident years earlier. Assistant Commissioner John Hartley, Commander of Traffic and Highway Patrol said the government backed its guidelines on detection windows. "Our pharmacologists tell us that for cannabis active for THC in saliva about 12 hours is the maximum it will be in their system and the maximum we would be getting a positive result on." A Department of Transport spokesperson told the Herald detection times "are based on the manufacturer's specifications for the MDT screening device and the latest medical research about how long drugs remain in a person's saliva after drug use".

When the Herald asked the manufacturer of the Draeger DrugTest 5000 - the machine used by the NSW police force to confirm an initial positive roadside swab - what advice on detection windows it provided clients, a spokesperson said it provided none and referred its clients to independent clinical studies. One study the Herald was directed towards by the company, found that while the median last detection time for occasional smokers was 12 hours it could be as long as 30 hours for those who smoked more than four times a week when tested with the Draeger DrugTest 5000. The co-author of that study Dr Dayong Lee, an American toxicologist who has published extensively on cannabis detection in oral fluid, told the Herald the 12-hour window advised by the NSW government was too narrow. "A person can definitely be positive after 24 hours at a concentration higher than 5 nanogram per milliliter." Assistant Commissioner Hartley would not reveal what concentration the NSW police were testing for. But on its website the Draeger DrugTest 5000 is marketed as having "extremely low detection rates", which can detect cannabis in concentrations of 5 nanograms per millilitre.

Dr Lee, whose studies have been approved by the US National Institute of Drug Abuse, said even occasional smokers could test positive at 21 hours. According to the latest research, THC levels can be as high as 1000ng per millilitre in a smoker's oral fluid directly after smoking but rapidly drop off within a few hours, she said. For chronic smokers, it can take up to 22 -24 hours to drop below 10 nanograms per millimetre, she said "The problem is it [the test] can positive for several hours and days at low concentrations for people who have been smoking cannabis for a long time." But Mr Barns said the zero tolerance approach made the laws "one of the most unfair on the statute books".

"It is patently unfair for someone who has driven impeccably to lose their licence simply because they have a trace of a substance that the government makes illegal, in their system." with Nick Ralston