As more states legalize marijuana for medical and recreational use, more drivers are likely to be driving under the influence. As stoned drivers get behind the wheel, questions and concerns about their mental impairment and the risks of increased dangers on the road are being discussed by law enforcement and state officials across the country.

Studies conducted by the National Highway Traffic Safety Administration show that 12 percent of drivers who are randomly stopped on weekends on U. S. roads and highways have been drinking alcohol. According to statistics, a standard field sobriety test conducted by law enforcement at the stop catches at least 88 percent of drivers under the influence of alcohol, but stoned drivers often pass the same test. Only 30 percent of people under the influence of THC, the active ingredient in marijuana, fail the field sobriety test. It appears that the ability to identify a stoned driver on the road depends heavily on the quantity and frequency of marijuana use.

According to the National Institute on Drug Abuse, marijuana use clearly causes deficits that affect driving ability, but THC has a different effect than alcohol. While drunk drivers tend to overestimate their abilities and drive faster, stoned drivers realize that they’re impaired and slow down. Laboratory drug studies reveal that most stoned individuals can pass simple tests of memory, addition and subtraction, but the real deficits of marijuana use show up when they have to handle multiple tasks at once or are confronted with something unexpected. This factor raises many concerns about stoned drivers on the road.

Testing the impairment level of a stoned driver on a routine stop is almost impossible with a field sobriety test. As George Bochanis, a Las Vegas auto accident lawyer points out, “a breathalyzer can reliably test blood-alcohol content on the side of the road, but THC levels must be measured with a urine or blood test, which is typically taken hours after an arrest. Urine tests often return positive results days, or even weeks after a person has smoked marijuana.”