More than 11,000 people have been caught driving under the influence of drugs since the start of the year, a rise of 30% since last year.

Figures obtained from police by ad.nl showed that drug-driving, including people who are over the limit for both alcohol and drugs, is now more common than drink-driving alone.

Police have stepped up roadside tests for drug use in response to the rising trend, but a spokesman said this did not fully explain the increase in positive tests. “It could be the case, but I don’t see any specific reason to think so,” he said.

Police use saliva tests to detect the presence of drugs and can commission a blood test from a laboratory if the roadside test gives a positive result.

Information service TeamAlert is launching an awareness campaign next month to warn young drivers of the dangers of taking drugs before getting behind the wheel.

In a survey of young people’s attitudes to drugs, nine out of 10 respondents said driving under the influence was wrong. But the organisation said many people wrongly believed drugs could have a positive influence, either by improving concentration or calming their nerves.

Lasting effect

Some drugs stay in the body longer than alcohol: ecstasy can produce a positive test up to 40 hours after being consumed, while frequent cannabis users are advised to wait at least a day before driving.

The Trimbos Institute, which specialises in addiction and mental health, said many drivers were unaware how long drugs can impair their performance on the road.

“On the one hand there are people who know they are under the influence but still think they’re good to drive,” said drugs researcher Steven Biemans.

“On the other hand there are people who think they’re no longer influenced by drugs because they’re no longer high.”

Trimbos advised young people travelling to summer festivals to name a designated driver, or “drugs bob”, who abstains from taking drink or drugs. “And make sure if you’re going to a festival for several days that ‘bob’ gets enough sleep,” Biemans said.