Calgary police say they like what they see in the proposed changes to Alberta's impaired driving laws in preparation for legalized recreational marijuana.

Under Bill 29, introduced in the legislature Tuesday by Transportation Minister Brian Mason, people charged with impaired driving would face a 90-day licence suspension.

The bill also proposes changes to the Traffic Safety Act to add cannabis impairment to existing provincial legislation on impaired driving.

The changes are being made to ensure provincial legislation complies with C-46, the federal impaired driving bill. It's also a response to a May 2017 ruling from the Alberta Court of Appeal that indefinite licence suspensions imposed by the province violated the Canadian Charter of Rights and Freedoms.

That practice ignored the presumption of innocence and the right to a fair trial before any punishment is imposed, the appeal court said.

THC limits planned

Under the new legislation, there will be limits to the amount of THC — the main psychoactive component that provides pot's high — that drivers can have in their system.

And there will be zero tolerance for either drugs or alcohol for drivers holding graduated licences.

Acting Sgt. Andrew Fairman with the Alcohol and Drug Recognition Unit says the province seems to be on the right track.

"Anything that we can do to improve our ability to detect and prosecute drug-impaired drivers is going to certainly assist, and from what I've seen of the legislation — we'll have to wait and see what comes out of the federal government — but I don't see how we could go any further at this point," he said.

The federal government is testing a device that would allow police to conduct roadside tests for impairment by cannabis, cocaine and methamphetamine. These devices test the saliva of suspected impaired drivers.

Until those devices are approved, police can charge a suspected drug-impaired driver based on observed behaviour and standard field sobriety tests.

Medicine Hat Police Chief Andy McGrogan, who is the Alberta representative for the Canadian Association of Chiefs of Police, told the Calgary Eyeopener on Wednesday that he and his counterparts hope a simple and reliable test to determine cannabis impairment is developed soon.

'New territory'

"It's new territory for us. We're just trying to brace for whatever's to come," he said. "We need the science behind this to prove, when someone is caught driving, that their impairment levels can be measured in real time," he said.

McGrogan says that when marijuana is legalized next summer he expects more drivers to be consuming.

Ian Savage, head of the Calgary Criminal Defence Lawyers Association, says he expects there will be legal challenges to Alberta's new law, partly because there is no scientific consensus on how much THC content constitutes impairment in a person.

"THC stays in your bloodstream for upwards of a month after consumption, and if you can't connect the cannabis consumption to some discernible way of detecting impairment, then what are you doing sanctioning it, and making it illegal," he said.

Savage is also troubled by plans for an immediate 90-day licence suspension for people charged with impaired driving, and the proposal for drivers to get their licence back by joining an ignition interlock program for one year.

Savage says that in many cases, drivers are acquitted or charges against them are withdrawn. Yet, those people would still be obliged to use the interlock device.

The Alberta government plans to hold public information sessions on the dangers of driving while under the influence of cannabis.

With files from the Calgary Eyeopener