Like so many other things, the short answer is, it depends.
A 2017 study in France found that drivers under the influence of alcohol were over 17 times more likely to be responsible for fatal car crashes than drivers who were sober. That same study found that drivers under the influence of weed were “only” 1 to 2 times more likely to do the same. So, does that make driving while intoxicated with THC safer than that of alcohol? While some might interpret the study by claiming driving high isn’t as dangerous as driving while drunk, it doesn’t make high driving safe by any means.
Additionally, it gets complicated when determining just how long cannabis affects the body, since THC can stay in one’s system for nearly a month, long after the high is gone. As a result, this can skew test results and create inaccuracies in studies.
Then you have to consider forms of cannabis such as edibles, and how THC onset times can vary widely and be very unpredictable. So, you might consume an edible, not feel anything for a while, then it hits you like a ton of bricks when you’re behind the wheel 45 minutes later.
The bottom line is that “safe” is not the right word to use when talking about driving while high. It’s not always as risky as driving while ingesting other substances, including alcohol, but it’s never going to be safe. If you want safe, take an Uber instead.