When Canada legalized cannabis in October 2018, there were many concerns about its potential impacts. One of them involved cannabis-impaired driving.

Before legalization, police were already catching more drug-impaired drivers each year. So, people naturally worried that more stoned drivers would appear on the road after legalization.

To lower that risk, the federal government updated its driving laws. Impairment by alcohol or drugs separately was already illegal. In December 2018, Canada also banned impairment by combinations of alcohol and drugs, or by unspecified substances.

Read more: Cannabis-impaired driving: Here’s what we know about the risks of weed behind the wheel

The government likewise helped police to better enforce those laws. For example, it gave them more power to obtain breath and blood samples from drivers. And it funded more training to help them recognize symptoms of drug impairment.

However, it was unclear how much........

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