Nearly half of drivers who die in road crashes have alcohol and/or drugs in their system, according to an Environment, Science and Research (ESR) report.

The report completed for the New Zealand Police and looking into the extent drugs played in driver deaths was a wake up call for road safety, the Automobile Association said today.

The five-year study looked at 1046 drivers who died between 2004 and 2009 (89 per cent of dead drivers during that time).

They were tested for alcohol and drugs and nearly half (48 per cent or 500 drivers) tested positive.

"Of those, 72 per cent or 365 drivers had either used cannabis, alcohol and cannabis, or a combination of drugs", AA's general manager for motoring affairs Mike Noon said.

The report showed that:

* 135 (27 per cent) had used alcohol alone;

* 96 (19 per cent) had used cannabis alone;

* 142 (28 per cent) had used both alcohol and cannabis; and

* 127 (25 per cent) had used a combination of drugs, which may have included alcohol and/or cannabis.

Mr Noon said the results showed that simply focussing on alcohol and drink driving would not address the problem of dangerously impaired drivers on our roads.

The ESR report said that "...when alcohol and impairing drugs are used together the effects are likely to be greater than when just one is used by itself".

"People with drugs in their system can currently go undetected. They might pass an alcohol roadside breath screening test and not be suspected for drugs, but their driving may be seriously impaired by drugs," Mr Noon said.

Only drivers who were grossly drug impaired were now detected by police at the roadside and were required to undertake an impairment test.

"This report shows we need better drug testing of drivers," Mr Noon said.

"The AA thinks it's time to consider increasing New Zealand's drug testing to include roadside saliva tests as is done in some Australian States."

The recent introduction of the roadside impairment test was a good first step to combat drugged driving, but this report had shown that it was nowhere near enough to detect and discourage drugged drivers as a third of drivers tested who died over the past five years had taken drugs, Mr Noon said.

The report also provided useful research data on driver BAC levels from the actual testing of drivers from fatal crashes and helped inform the current debate on whether to lower the adult BAC level from 80mg to 50mg of alcohol per 100ml of blood.

The majority (81 per cent) of dead drivers in the study were considered to have been at fault for their crash.

"The report confirms that the problem of driver impairment on our roads is a serious one and much wider than just alcohol," Mr Noon said.