How Does Marijuana Affect Driving?
Many people understand the dangers of drinking and driving, but are not aware of the significance of marijuana use and driving. Marijuana affects many skills required for safe driving: alertness, concentration, coordination, and reaction time. Marijuana use can make it difficult to judge distances and react to signals and sounds on the road. Data shows that marijuana can play a role in motor vehicle crashes. Studies show that approximately 4-14 percent of drivers who sustained injury or died in traffic accidents tested positive for THC (the active ingredient in marijuana). When users combine marijuana with alcohol, as they often do, the hazards of driving can be more severe than with either drug alone. In a study conducted by the National Highway Traffic Safety Administration, a moderate dose of marijuana alone was shown to impair driving performance; however, the effects of even a low dose of marijuana combined with alcohol were markedly greater than those of either drug alone. In one study conducted in Memphis, Tennessee, researchers found that, of 150 reckless drivers who were tested for drugs at the arrest scene, 33 percent tested positive for marijuana, and 12 percent tested positive for both marijuana and cocaine. Data also show that while smoking marijuana, people display the same lack of coordination on standard "drunk driver" tests as do people who have had too much to drink.