A recent study from our group in collaboration with the Lambert Initiative at Sydney University shows that THC-dominant cannabis can cause impairment of on-road driving and cognitive function for up to 4 hours after vaporization. Cannabis that contained CBD only did not affect driving and cognition. Cannabis that contained both THC and CBD produced impairment levels similar to cannabis with THC only. Read the full paper as published in JAMA.
https://jamanetwork.com/journals/jama/fullarticle/10.1001/jama.2020.21218