The number of fatal crashes in Washington involving drivers who tested positive for cannabis has more than doubled in the years since marijuana was legalized, according to a new study.

Around 50 drivers involved in fatal crashes in the five years before Initiative 501 was enacted in 2012 tested positive for THC. Since the law to legalize recreational use of cannabis was enacted, however, the number of THC-positive drivers involved in fatal crashes jumped to 130, according to the American Automobile Association, using Washington Highway Traffic Commission data.

THC is the main psychoactive component in cannabis, and its detection suggests recent or frequent use, according to the study.

“The number of THC-positive drivers involved in fatal crashes in Washington is alarmingly high,” said Matthew Conde, public information officer for AAA in Idaho.

Before the law took effect, an average of 9 percent of all drivers in fatal crashes statewide tested positive for marijuana, Conde said. The number ballooned to 21 percent in 2017.

The study doesn’t point fingers, Conde said. It does, however, reflect an increase in the number of motorists who drive with THC in their system, and that drivers with THC in their blood stream may be a crash risk.

“We’re not saying that the person with the THC was the culprit every time,” Conde said. “It may be that they weren’t at fault.”

Trooper Jeff Sevigney, who works in Washington’s District 4, which includes Spokane County, has seen the uptick.

Before the initiative took effect in late 2012, Sevigney said, fewer people who were stopped for impaired driving, or who were involved in crashes, were high on THC.

If the results of a breath test showed negative for alcohol, Troopers would draw blood to see if drivers were impaired, he said. The blood evidence is used in court.

Laws regarding blood draws have changed, Sevigney said. Police must now secure a warrant from a judge, which is done electronically in minutes. The results of blood draws have shown a jump in THC use among impaired drivers.

“We’ve definitely seen an increase,” Sevigney said.

Just as driving with a blood alcohol level above .08 is illegal, driving with a THC level above .5 nanograms is against Washington law, he said.

Conde said THC can play a role not just in the cause of a crash, but in failing to avoid a crash.

“Marijuana can cause decreased reaction time and attentiveness — a dangerous combination while operating a motor vehicle,” Conde said.

The data shows that drivers with THC in their system can double a driver’s odds of causing a wreck, he said.

Other studies, including one by the Highway Loss Data Institute, which collects data for insurance companies, show that the legalization of recreational marijuana in Washington, Colorado and Oregon is associated with a jump in the number of automobile collision claims compared to states where marijuana remains illegal.

Conde said the latest study is important if only to draw attention to the negative effects of cannabis use.

”It raises the question, how are we dealing with this issue?” he said.

Sgt. Darren Wright at the Washington State Patrol’s Olympia office said his agency reviewed the AAA report and found the statistics to be accurate.

“It’s valid,” he said.