Senate struggles with key question: How do you measure pot impairment for drivers? Bill Blair, Parliamentary Secretary to the Minister of Health, sits in a driving simulator meant to simulate the effects of driving under the influence of cannabis, during a photo opportunity at Centre for Addiction and Mental Health (CAMH) in Toronto on Wednesday January 24, 2018. Chris Young

Senate struggles with key question: How do you measure pot impairment for drivers? Bill Blair, Parliamentary Secretary to the Minister of Health, sits in a driving simulator meant to simulate the effects of driving under the influence of cannabis, during a photo opportunity at Centre for Addiction and Mental Health (CAMH) in Toronto on Wednesday January 24, 2018. Chris Young