Motor vehicle accidents are the leading cause of death for young people, and up to 40% involve substance-related impairment. To better understand the factors contributing to impaired driving in this age group, investigators administered anonymous questionnaires to 994 urban and 1600 rural 10th and 12th grade students on Vancouver Island, Canada. Of the sample, 1192 students had driving permits that required adult supervision and limitations on the number of nonrelatives in the car.

• Just over half of students reported riding in a car with an adult who had been drinking, and one-fifth to one-third reported driving with an adult who had smoked cannabis.
• One-fifth to one-third of students reported riding with a peer driver who had been drinking, and about one-third had ridden with a cannabis-impaired peer driver.
• Of students with driving permits, up to one-fifth reported driving after drinking or after smoking cannabis. More favorable attitudes towards these substances were associated with increased driving after use.
• Riding with impaired peers was independently associated with increased driving after substance use.
• Driving after substance use was highest in youth who reported more frequent experiences of riding with adults who drank alcohol or used cannabis while driving.

Comments by Tom Delaney, MSW, MPA
Although this large study analyzes how drug use and drinking behavior by adults can influence the driving decisions of young people, it has important implications for the prevention and treatment of alcohol and drug addiction in other populations. Peers influence many decisions across the life span. This article reminds counselors of the importance of recognizing the role of peer influence in treatment and prevention.

Comments by Peter D. Friedmann, MD, MPH, Associate Editor, Alcohol, Other Drugs, and Health: Current Evidence
The influence of peers and parents on adolescent behavior is well-described, but this study suggests that peer and adult modeling of risky driving has synergistic effects on adolescents' likelihood of impaired driving. Although this study cannot discern whether the adults drove after drinking "under the limit," children riding with them are unlikely to make such distinctions. In addition to counseling teens about the dangers of driving alone or with peers under the influence of drugs or alcohol, physicians are in a good position to counsel parents about driving after substance use and its risks to themselves and their children, regardless of amounts.