The Edmonton Police Service says the impact of cannabis legalization has been lower than expected as the latest numbers show a slight rise in drug-impaired driving arrests.

Police suspect cannabis contributed to 39 drug-impaired driving arrests in the first 10 months of 2019, compared to 33 arrests over the same period in 2018.

But in a report going to city councillors next week, police say they expect the numbers to rise as cannabis supply grows and edibles hit the market.

As of Nov. 10, police made 134 drug-impaired driving arrests in 2019, according to the report. That's a 17-per-cent increase over 2018, when police arrested 115 drug-impaired drivers.

Police have said more training and resources are responsible for the consistent rise in impaired driving arrests, more so than legal cannabis. Since 2015, there's been a more than 10-fold increase in the number of officers who can administer roadside sobriety tests in Edmonton.

The report says 759 frontline officers have now been trained on new cannabis legislation.

While arrests have increased, the share of suspected cannabis-related cases has been steady over the past two years at around 29 per cent of drug-impaired driving arrests, the report shows.

But police say the full impact of legal cannabis on policing has only just started to emerge.

For one, the report notes a limited supply of cannabis cooled the retail market in Alberta for the first half of 2019. As supply increased, Alberta Gaming, Liquor and Cannabis lifted a moratorium on retail licenses in May. Edibles, meanwhile, only hit the shelves of Edmonton cannabis stores last month.

Edmonton police present a quarterly cannabis report to city councillors on the impact of legalization and the actual costs. (The Canadian Press)

To support the police response to legalization, city council approved $1.4 million in funding for EPS in May 2018. When police came back a few months later asking for $3 million to hire 24 cannabis patrol officers, council turned down the request, asking police to provide quarterly updates on the community impact and financial cost of legalization.

The latest quarterly report says policing drug-impaired driving is costly. Police say it takes six times longer, and costs six times more, to process a cannabis-impaired driver compared to a driver impaired by alcohol. It costs on average $537 to process a drug-impaired driver.

Drivers who fail a field sobriety test can be arrested for impaired driving. The driver is then taken to a trained drug recognition expert to perform a 12-step test. If they fail, Edmonton police demand a blood or urine sample and wait for the results, which can take several months, before laying charges.

The report says Edmonton police conducted around 30 roadside checkstop campaigns in 2019.

It will go to the community and public services committee on Feb. 12.