the drug is the second most frequently found substance in the bodies of drivers involved in fatal motor vehicle accidents after alcohol.

I suspect if they had a control group for this, they would find it is also the second most frequently found substance in the bodies of everyone everywhere, after alcohol.

Seems like an Arse Covering Study, to avoid further lawsuits later.

Alcohol: Be under an amount we have decided constitutes an impairment in your cognitive and motor skills.

Cannabis: Be under an amount based on what our tests can detect, often several days after last consumption.