Marijuana-impaired drivers growing in number

Drivers under the influence of marijuana are becoming alarmingly common on the roads of Georgia and other U.S. states according to a study from the National Highway Traffic Safety Administration. The agency's National Roadside Survey of Alcohol and Drug Use by Drivers suggests that the number of marijuana-impaired drivers has increased dramatically, and tests conducted at 60 sites across the country in 2013 and 2014 found traces of the drug in samples collected from 9 percent of daytime drivers and 13 percent of nighttime drivers.

NHTSA has been studying driver impairment trends since the 1970s. Alcohol was the primary focus of the agency's National Roadside Studies until drug screening was introduced in 2007. The results of the latest study were discussed at a meeting of the Research Society on Alcoholism.

Marijuana-impaired drivers present police departments with a thorny problem. Research shows that alcohol and marijuana impair drivers in different ways, and law enforcement training that is designed to help officers to identify drunk drivers may be of little use when motorists are under the influence of marijuana. While drivers who have been drinking often exceed speed limits or run red lights, motorists under the influence of marijuana tend to drive more slowly and deliberately.

Experienced criminal defense attorneys may urge prosecutors to consider reducing or dropping impaired driving charges when marijuana is involved and the evidence against their client is based on toxicology testing and the observations of police officers. Defense attorneys could point out to prosecutors that THC can be detected in blood samples long after its intoxicating effects have dissipated. Prosecutors must establish proof beyond any reasonable doubt, and that may be difficult for them to accomplish in these cases without compelling scientific evidence.