As calls to legalise or at least decriminalise cannabis in New Zealand grow, politicians will no doubt be watching what happens in Canada – which this week legalised recreational cannabis ­– closely.

A report from the US National Transportation Safety Board has determined a March 2017 crash near Concan, Texas was caused by a 20-year-old driver‘s failure to control his vehicle due to his use of cannabis in combination with misuse of a prescription medication.

The deadly crash occurred when the driver of a pick-up traveling northbound on US Highway 83 crossed the double, solid-yellow centreline and collided with a bus carrying 13 passengers. Witnesses observed the pick-up driver driving erratically for more than 15 minutes prior to the collision. The bus driver and 12 of the 13 passengers were killed, and the driver of the pick-up and one of the bus passengers suffered serious injuries.

The post-crash inspection of the pick-up truck‘s cab revealed unsmoked and partially smoked cannabis cigarettes, drug paraphernalia, and prescription and over-the-counter medication. Among the drugs identified in the pick-up driver‘s post-crash toxicology test were Delta-9-THC, a primary active chemical in cannabis, and clonazepam, a sedative used to treat seizure and panic disorders. The driver stated he took twice his prescribed dosage of clonazepam prior to the crash.

The NTSB report also noted the prevalence of illicit, prescription and over-the-counter drug use among drivers is increasing. The NTSB determined national leadership is needed to help identify science-based countermeasures that can be implemented at the state and local levels to prevent future similar tragedies.

“The pick-up truck driver in this crash made terrible choices with tragic consequences,” said NTSB chairman Robert L. Sumwalt. “But the rising tide of drug-impaired driving did not begin with this driver, and it will not end with him. Law enforcement needs additional tools and advanced training to detect impaired drivers before they crash, regardless of the impairing drug they‘re using.”

The NTSB also determined the state of Texas needs increased safety-focused leadership, additional resources, and data-driven strategies to prevent future impaired driving crashes and fatalities. Additionally, to better understand the extent of the drug-impaired driving problem, the NTSB called on the National Highway Traffic Safety Administration to develop a common standard of drug toxicology testing.

As a result of this investigation the NTSB issued a number of recommendations to the National Highway Traffic Safety Administration, including a recommendation to develop and disseminate best practices and model specifications for oral fluid drug screening devices that can be used by law enforcement during roadside stops.