I remember an article on this in New Scientist back in the 90s that went into a lot more depth. A study showed that while alcohol impaired multiple aspects of

I remember an article on this in New Scientist back in the 90s that went into a lot more depth. A study showed that while alcohol impaired multiple aspects of driving skill marijuana mostly impaired just time judgement. And stoned drivers tended to overestimate their level of impairment and slow down while drunk drivers tended to underestimate how impaired they were. They actually found that drivers who were moderately drunk and stoned were less likely to crash than drivers who were just moderately drunk because they slowed down even though they were more impaired.