TORONTO -- Ontario's two largest police forces have stepped up training for their officers to better detect drugged driving as legislation on legalizing marijuana looms in Ottawa.

Both Toronto police and Ontario Provincial Police are waiting to pore over the federal government's much-anticipated pot bill, which is expected to be tabled on Thursday, with a keen eye on provisions around impaired driving related to the drug.

In Toronto, about a dozen officers are being trained each month in field sobriety testing, a series of physical movements used by police to test for drug impairment, according to Const. Clint Stibbe of the force's traffic services. There are already about 200 officers trained in that area, he said.

The force is also expanding its team of drug recognition evaluators -- officers who interview and further test individuals who have been arrested on suspicion of drugged driving.

One new officer will be added to the team this year, and three more will be added next year, Stibbe said, noting there are currently 15 drug recognition evaluators on the force. One is available 24 hours a day.

The Toronto team is part of more than 200 drug recognition evaluators across the province, the Ontario Provincial Police said.

OPP Sgt. Peter Leon said the provincial force has 85 such officers of its own and more are being trained every month.

While both Stibbe and Leon were leery of predicting the future given the unknowns of the upcoming marijuana legislation, they were bracing for an uptick in drugged driving.

"We really hope we don't see a rise in impaired driving because of marijuana legalization, but we have to prepare as if we will see an increase," Leon said.

Stibbe agreed.

"We are erring on the side of caution and expect to see a rise," he said. "But we've already seen a rise in drug-impaired driving, from 24 arrests in 2015 to 86 arrests last year, which is a three-fold increase. That increase could also be explained by better training and detection on our officers part, though."

Data from Toronto police indicates, however, that drugged driving in Canada's most populous city represents a fraction of overall impaired driving arrests, while alcohol impairment remains number one with 1290 arrests in 2016.

Stibbe also noted that marijuana isn't the top drug detected in the force's impaired arrests -- central nervous system depressants that include benzodiazepines and anti-psychotic medication take that spot.

Currently, field sobriety testing and drug recognition evaluators are two main pillars of testing for detecting drugged driving, Leon said.

The field testing includes a walk and turn, standing on one leg and an eye gazing test.

The drug recognition evaluators can conduct comprehensive interviews with further testing to figure out whether an individual is under the influence of an illegal drug, a prescription drug or having a medical episode. Urine is then taken and sent to the Centre of Forensic Sciences, which tests for a litany of substances.

Police may also have another tool at their disposal in the future to help fight drugged driving: roadside screening devices.

The OPP, Toronto police and the RCMP were involved in a recently concluded pilot program under direction of Public Safety Canada that tested roadside drug testing devices.

On Tuesday, Toronto police released preliminary data from the program that showed of the 208 people they tested -- who were volunteers because legislation would have to be passed to use the devices -- nine tested positive for drugs.

Four tested positive for cocaine while three tested positive for marijuana.

The devices used either a swab or a wipe that took fluid from an individual's mouth and then entered it into the device. About seven minutes later, the device would print out the results.

Stibbe said the volunteers were only tested after all other impairment tests proved negative -- and some were conducted on passengers.

"Much of the pilot program was designed to test the devices in real world situations," Stibbe said.

He said the device would be helpful in certain situations where a front-line officer isn't sure if an individual is impaired.

A report on cannabis policy prepared for Public Safety Canada notes that the methods of detecting drugs in the human body are "still far from perfect."

It said chemical traces of cannabis remain in blood for longer periods than alcohol, so fatally-injured drivers who test positive for cannabis may not actually have been operating a vehicle while intoxicated.

The report, released last year, says that while methods for assessing alcohol impairment, collecting evidence, and legal thresholds for impairment have been clearly delineated, the situation is much less clear in the case of cannabis.

It said a key concern is the quality of training of law enforcement officials in collecting evidence of impairment and developing ways to measure for the presence of cannabis metabolites in the body.