Drugs on the Roads

How Many People Take Drugs and Drive?

ANS: According to the National Highway Traffic Safety Administration’s (NHTSA) 2007 National Roadside Survey, more than 16 percent of weekend, nighttime drivers tested positive for illegal, prescription, or over-the-counter medications.

More than 11 percent tested positive for illicit drugs.1 Another NHTSA study found that in 2009, among fatally injured drivers, 18 percent tested positive for at least one drug (e.g., illicit, prescription, or over-the-counter), an increase from 13 percent in 2005.2

Together, these indicators are a sign that continued substance abuse education, prevention, and law enforcement efforts are critical to public health and safety.

According to the 2009 National Survey on Drug Use and Health (NSDUH), an estimated 10.5 million people aged 12 or older reported driving under the influence of illicit drugs during the year prior to being surveyed.3 This corresponds to 4.2 percent of the population aged 12 or older, similar to the rate in 2008 (4 percent) and not significantly different from the rate in 2002 (4.7 percent). In 2009, the rate was highest among young adults aged 18 to 25 (12.8 percent). In addition, NSDUH reported the following:

  • In 2009, an estimated 12 percent of persons aged 12 or older (30.2 million persons) drove under the influence of alcohol at least once in the past year. This percentage has dropped since 2002, when it was 14.2 percent.
  • Driving under the influence of an illicit drug or alcohol was associated with age. In 2009, an estimated 6.3 percent of youth aged 16 or 17 drove under the influence. This percentage steadily increased with age to reach a peak of 24.8 percent among young adults aged 21 to 25. Beyond the age of 25, these rates showed a general decline with increasing age.
  • Also in 2009, among persons aged 12 or older, males were more likely than females (16.9 percent versus 9.2 percent, respectively) to drive under the influence of an illicit drug or alcohol in the past year.

In recent years, more attention has been given to drugs other than alcohol that have increasingly been recognized as hazards to road traffic safety. Some of this research has been done in other countries or in specific regions within the United States, and the prevalence rates for different drugs used vary accordingly. Overall, marijuana is the most prevalent illegal drug detected in impaired drivers, fatally injured drivers, and motor vehicle crash victims. Other drugs also implicated include benzodiazepines, cocaine, opiates, and amphetamines.4

A number of studies have examined illicit drug use in drivers involved in motor vehicle crashes, reckless driving, or fatal accidents. For example—

  • One study found that about 34 percent of motor vehicle crash victims admitted to a Maryland trauma center tested positive for “drugs only;” about 16 percent tested positive for “alcohol only.”
  • Approximately 9.9 percent (or 1 in 10) tested positive for alcohol and drugs, and within this group, 50 percent were younger than age 18.5 Although it is interesting that more people in this study tested positive for “drugs only” compared with “alcohol only,” it should be noted that this represents one geographic location, so findings cannot be generalized. In fact, the majority of studies among similar populations have found higher prevalence rates of alcohol use compared with drug use.6

Studies conducted in several localities have found that approximately 4 to 14 percent of drivers who sustained injury or died in traffic accidents tested positive for delta-9-tetrahydrocannabinol (THC), the active ingredient in marijuana.7

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  • In a large study of almost 3,400 fatally injured drivers from three Australian states (Victoria, New South Wales, and Western Australia) between 1990 and 1999, drugs other than alcohol were present in 26.7 percent of the cases.8 These included cannabis (13.5 percent), opioids (4.9 percent), stimulants (4.1 percent), benzodiazepines (4.1 percent), and other psychotropic drugs (2.7 percent). Almost 10 percent of the cases involved both alcohol and other drugs.

Teens and Drugged Driving

According to the Centers for Disease Control and Prevention, vehicle accidents are the leading cause of death among young people aged 16 to 19.9 It is generally accepted that because teens are the least experienced drivers as a group, they have a higher risk of being involved in an accident compared with more experienced drivers. When this lack of experience is combined with the use of marijuana or other substances that impact cognitive and motor abilities, the results can be tragic.

Results from NIDA’s Monitoring the Future survey indicate that in 2007, more than 12 percent of high school seniors admitted to driving under the influence of marijuana in the 2 weeks prior to the survey.10

The 2007 State of Maryland Adolescent Survey indicates that 11.1 percent of the State’s licensed adolescent drivers reported driving under the influence of marijuana on three or more occasions, and 10 percent reported driving while using a drug other than marijuana (not including alcohol).11

Why is Drugged Driving Hazardous?

Drugs acting on the brain can alter perception, cognition, attention, balance, coordination, reaction time, and other faculties required for safe driving. The effects of specific drugs of abuse differ depending on their mechanisms of action, the amount consumed, the history of the user, and other factors.

Marijuana

THC affects areas of the brain that control the body’s movements, balance, coordination, memory, and judgment, as well as sensations. Because these effects are multifaceted, more research is required to understand marijuana’s impact on the ability of drivers to react to complex and unpredictable situations. However, we do know:

  • A meta-analysis of approximately 60 experimental studies—including laboratory, driving simulator, and on-road experiments—found that behavioral and cognitive skills related to driving performance were impaired in a dose-dependent fashion with increasing THC blood levels.12
  • Evidence from both real and simulated driving studies indicates that marijuana can negatively affect a driver’s attentiveness, perception of time and speed, and ability to draw on information obtained from past experiences.
  • A study of over 3,000 fatally injured drivers in Australia showed that when marijuana was present in the blood of the driver, he or she was much more likely to be at fault for the accident. Additionally, the higher the THC concentration, the more likely the driver was to be culpable.13
  • Research shows that impairment increases significantly when marijuana use is combined with alcohol.14 Studies have found that many drivers who test positive for alcohol also test positive for THC, making it clear that drinking and drugged driving are often linked behaviors.