A recent report from the National Highway Traffic Safety Administration suggests that the number of marijuana-impaired drivers in Wisconsin and around the country has increased by about 50 percent in only seven years. The agency’s 2013 and 2014 National Roadside Survey of Alcohol and Drug Use by Drivers also reveals that traces of THC, which is the chemical compound in marijuana that causes impairment, were found in the oral fluids or blood of 13 percent of the nighttime drivers who participated in the study and 9 percent of the daytime drivers who were tested.
NHTSA has been conducting National Roadside Studies since the 1970s, but the agency did not begin to test motorists for drug-related impairment until 2007. These studies are based on breath, blood and oral fluid samples collected from drivers at 60 locations spread across the United States, and their results are used to help shape future safety regulations and law enforcement initiatives. Alcohol intoxication among drivers has fallen by more than three-quarters since 1977 according to NHTSA, but the agency says that marijuana impairment is on the rise due largely to the passage of laws in many states that allow the drug to be used for medical or recreational purposes.
The use of marijuana presents lawmakers and police officers with a number of challenges. THC affects individuals differently to alcohol, and techniques designed to identify drunk drivers may be of little use when motorists are impaired by marijuana. Alcohol-impaired drivers often act recklessly and behave aggressively, but motorists under the influence of THC tend to slow down and drive more deliberately.
Experienced criminal defense attorneys may seek to have drunk driving cases dismissed when their clients are accused of driving under the influence of marijuana and the evidence against them is unconvincing. Toxicology test results are usually crucial in these cases, and attorneys may point out to prosecutors that scientists have yet to find an effective way to measure THC impairment.