"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.

The U.S. Department of Transportation (DOT) is advising that all safety-sensitive workers must still comply with federal drug testing requirements, even as the president directs the attorney general to complete a cannabis rescheduling process.

The executive order is significant to the cannabis industry for its support of more research, stronger standards and ending negative stereotypes.