"This risk is exacerbated by the fact that there is currently no proven, widely accepted standard to determine marijuana impairment at the roadside or before a driver begins operating a vehicle, making it far more difficult to prevent impaired driving," she added.

President Donald Trump signed an executive order urging the rescheduling of marijuana under federal law on Dec. 18. Here's what to know.

The move wouldn't legalize marijuana, but moving it from Schedule I to Schedule III would allow the FDA to study it for medical purposes.