Drivers under the influence of cannabis are twice as likely to be involved in a car crash.

This risk is particularly prevalent in cannabis users aged 35 or younger.

Researchers from Dalhousie University in Canada reviewed nine studies of almost 50,000 people involved in “serious” car crashes.

Drivers of cars, sports utility vehicles, vans, lorries, buses and motorcycles featured in the analysis.

Recent cannabis use was detected through blood samples or direct self report.

It was found that drivers who consume cannabis within three hours of getting behind the wheel double the risk of a crash.

The study, published in the BMJ, concludes the consumption of cannabis impairs motor tasks needed for safe driving.

According to road safety charity Brake, 18% of people killed in road crashes in the UK have traces of illegal drugs in their blood, with cannabis being the most common.

A recent survey by the charity found one in nine young drivers admitted driving on illegal drugs.

“Tackling drug driving should be a top priority,” said Julie Townsend, Deputy Chief Director of Brake.

“This report highlights the danger posed by drivers who have smoked cannabis and adds weight to Brake’s calls for widespread testing and prosecution of drivers who selfishly risk lives by taking illegal drugs and driving.

“We are pleased the government has expressed commitment to tackling drug driving; we now need urgent action to bring in this desperately needed change in the law – taking a tough, zero tolerance stance – and roadside screening devices to create a strong deterrent against this heinous and highly dangerous behaviour.”

Wayne Hall from the University of Queensland Centre for Clinical Research in Australia said it is “too optimistic” to assume roadside drug testing will “substantially reduce” road crash deaths.

“Public health education about the dangers of driving while under the influence of cannabis is also unlikely to be enough to deter cannabis users from driving—they will need to be persuaded that they are at risk of their cannabis use being detected,” Hall writes in the BMJ.

Question: Do you think roadside drug testing will deter people from driving while under the influence of drugs in the same way it has done for alcohol?