"And after adjusting for age, gender, race and alcohol use, drivers who tested positive for marijuana were no more likely to crash than who had not used any drugs or alcohol prior to driving."
Edit: Just in case in the future anyone comes across my comment out of context of this thread, I'd like to add that without seeing further research I'm not personally convinced by that statement.
Since testing positive just means that you might have used anytime in the past month or so, that's not meaningful.
The study linked in the article confirms that yes, according to the evidence seen, marijuana significantly impairs driving ability, especially among casual users (to the surprise of no one whose actually used it I'm sure).
"And after adjusting for age, gender, race and alcohol use, drivers who tested positive for marijuana were no more likely to crash than who had not used any drugs or alcohol prior to driving."
Edit: Just in case in the future anyone comes across my comment out of context of this thread, I'd like to add that without seeing further research I'm not personally convinced by that statement.