The "Drugs and Driving: Detection and Deterrence" report has been published by the International Transport Forum, a transport think tank at the OECD and is based on road-side tests, surveys and questionnaires from 16 countries.

According to the study, the incidence of drugs among drivers injured or killed in road accidents is in the range of 14% to 17%. Cannabis and benzodiazepines top the list of drugs involved in lethal motor accidents.

Other alarming findings of the report include:

• The prevalence of drug use by drivers in North America now rivals or exceeds that of drivers who have been drinking.

• Of over 500 high school students surveyed in Canada, 19.7% admitted to driving within an hour of using cannabis.

• 27% of over 3,400 drivers killed in road accidents in Australia had some form of drug in their body system. In 14% of cases it was cannabis.

• In a study of injured drivers in France, 14% of drivers also tested positive for cannabis.

• Drugs were found in over 40% of injured drivers in two groups tested in the Netherlands.

However, compared to drink driving, there are manifold issues involved with detecting drug drivers, including the fact that drugs can include prescription medication. This means that policy of "zero tolerance" can only target illegal drugs, not legal medication.

'There is not one drug with one effect, but multiple drugs with multiple effects on the human body,' said Jack Short, secretary general of the International Transport Forum. 'Both illicit substances and prescribed medicine are involved. Current drink-driving measures and legislation do not take this into account.'

Among the policy recommendations made by the report are:

• To seek international consensus on key substances that pose a risk to road safety.

• To establish a list of potentially impairing substances and label them with a warning.

• To focus on road safety rather than the prosecution of drug users.

• To train enforcement personnel in detecting signs and symptoms of drug use.

• To engage in more research on drugs and driving to ensure that policies are evidence-based.

The ITF also says that current projects into the issue of drugs and driving will help establish public policy along with enforcement and prevention measures. These include a major EU-funded research project called DRUID (Driving under the Influence of Drugs, Alcohol and Medicines) in Europe and a large-scale study being carried out in the US by the National Highway Traffic Safety Administration.

The executive summary of Drugs and Driving: Detection and Deterrence can be downloaded from www.internationaltransportforum.org