More than 200 police have been trained to conduct roadside tests on drivers suspected of being stoned behind the wheel.
The new regime of compulsory impairment tests begins on Sunday, the same day as 19 other transport rule changes - including a ban on using handheld cellphones while driving, and a requirement for riders of post-1979 motorbikes and mopeds to use headlights at all times.
National road police manager Superintendent Paula Rose says her staff will also be watching for people wearing seat-belts incorrectly, and vehicles being towed at more than the new speed limit of 50km/h.
Ms Rose said all front-line police would be expected to be alert for drivers impaired by illicit or prescribed drugs. The first course for police suspecting impairment would be to conduct alcohol breath tests.
But if a driver appeared the worse for wear despite remaining under the legal alcohol limit, a specialist officer trained to conduct compulsory impairment tests would be contacted.
A driver failing to pass a three-stage test - involving assessments of eye pupil sizes and co-ordination, walking and turning, and standing on one leg while counting down numbers - would have to submit to a blood test for evidence of illegal drugs or prescription medicines.
The idea of impairment testing has found an unlikely ally in the National Organisation for the Reform of Marijuana Laws [Norml].
Auckland co-ordinator Chris Fowlie said the organisation advocated "responsible cannabis use", and driving while impaired did not meet that standard.
But Mr Fowlie said the group feared the new law relied too much on the subjective opinions of police officers, who would single out stereotypical cannabis users.
They could then require drivers to submit to blood tests with a zero tolerance to cannabis residue, even if the drug had been consumed weeks or months earlier.
"So whether or not they were impaired at the time of driving, which should be the issue, it now becomes just another way to bust pot smokers simply because these residues hang around."
Mr Fowlie feared some cannabis users may instead switch to other substances, such as alcohol or P, because they tended to be flushed out of the bloodstream as their effects wore off.
Mr Fowlie said that although cannabis impaired driving, users tended to be more aware of their limitations than those under the influence of alcohol, and were likely to be more careful.
But Ms Rose said the impairment tests would be conducted professionally, and refrained from making any comment on the relative dangers of alcohol and other substances.
By Mathew Dearnaley
October 28, 2009
New Zealand Herald
Police ready for tests on suspected stoned drivers