Police are defending their policy of not carrying out random drug tests on drivers.
At present, an obviously impaired driver is breath-tested for alcohol and, if that is negative, blood-tested for drugs.
An Environmental Science Research report in 2010 on blood samples of drivers who died in crashes found that just 27% of those with alcohol or other drugs in their system were drunk. The rest were drugged, or drunk and drugged.
New Zealand's top road policing officer, Superintendent Paula Rose, says the lack of random saliva tests is due to a lack of faith in their accuracy.
Ms Rose says products are improving and her office will be reporting to the Government during 2012 on those developments.
The Automobile Association says it does not accept the police's rationale in refusing to conduct random drug testing.
General manager of motoring affairs Mike Noon says just 500 tests for drug-driving have been done in the past 18 months.
Mr Noon says it is naive to think that New Zealand's huge number of daily users of methamphetamine and cannabis are not also daily drivers.
The Automobile Association says random drug tests are used throughout Australia and will soon be introduced in Britain.