Positive drug drive test may not mean impairment, cops admit

THE NSW Greens have called for roadside drug testing to be abolished after obtaining classified police documents showing a positive reading does not mean a driver is under the influence of illicit drugs.

Upper House MP David Shoebridge said the tests had no lower limit for detection, meaning a person could be found guilty of driving with drugs in their system that may have had no impact on their driving abilities.

"Information obtained by the Greens through the freedom of information process has shown that the current roadside drug testing regime is arbitrary, invasive and has no relationship to the impairment of drivers on our roads," he said in a statement.

"The NSW police force strongly resisted the release of this information, and it was necessary to undertake an internal review to have the materials released.

"The public would have deep concerns that the NSW police force are laying charges, investigating and conducting prosecutions with no information on what exactly is tested for in roadside drug tests or at what levels."

The internal NSW Police documents state: "This program does not infer impaired driving or driving a motor vehicle under the influence of a drug. This program detects the presence of an illicit drug in a subject's oral fluid."

"Testing certificates received from the Forensic and Analytical Science Service do not disclose quantity as there is no prescribed quantity of drug to be tested for," it continues.

The National Cannabis Prevention and Information Centre says marijuana can affect driving ability for up to five hours.

"The length of time it stays in your system depends on a lot of things, but in general it may be found in urine for one to five days after occasional use and up to six weeks if you're a regular, long-term user," it says.

Drugs such as ice and heroin are much quicker to be flushed out of the body despite being considered more serious forms of illegal drug.

Drug testing frequency is set to skyrocket from a current 32,000 tests to 97,000 in 2017 as police ramp up the program.

The increase has the Centre for Road Safety's support after its researchers found 195 deaths on NSW roads between 2010 and 2013 involved drivers or riders with at least one of three illegal drugs - ecstasy, speed or marijuana - in their systems.

The centre found at least 13% of all road deaths involved a driver with drugs in their system - whether it impaired their driving, or not.

Australia has one of the highest rates of marijuana use in the world, with the Australian Institute of Health and Welfare finding 34.8% of people aged 14 or older had used the drug at least once.