There are too many variables to this question. A noob smoker blazed out of his brain trying to drive would probably be just as bad as a drunk driver. If you’ve been smoking for years, and overall have a tolerance built up as well as just being all and all more familiar with how marijuana affects you, I believe the risks can be substantially mitigated.

Reaction time is important but it’s not the only piece of the puzzle. Each person still has their own driving style which can range from aggressive with little respect for the rules of the road to a defensive driver that pays attention to his surroundings and respects traffic law. For example, a minor reaction time increase could have drastically different implications for a driver who likes to tailgate vs. one that leaves a reasonable multi-second gap.

For me, driving sober is extremely stressful and I freak out on a lot of stuff like entering a crowded freeway, going over tall bridges, driving near one of those cement barriers, etc. When I smoke and drive I spend less time stressed out about random shit and more time focused on the road.