Conference Coverage

Inexperience is the main cause of unsafe driving among teens


NEW ORLEANS – Teens need to drive for a wide range of reasons, from going to and from school or work to overall mobility, but driving still is the most dangerous thing teenagers do, according to Brian Johnston, MD, MPH, professor of pediatrics at the University of Washington in Seattle.

Teenage boy learning to drive Kali9/E+/Getty Images

Motor vehicle traffic accidents continue to be the leading cause of death of adolescents aged 15-19 years, according to 2017 data from the National Center for Health Statistics at the Centers for the Disease Control and Prevention.

“Inexperience drives the statistics we see,” Dr. Johnston said at the annual meeting of the American Academy of Pediatrics. “There is a steep learning curve among drivers of all ages, and crash rates are highest during the first few months after teens begin driving without supervision.”

Although the risk of accidents is higher than average for any new driver, it’s disproportionately higher for younger teens, compared with other ages: 16-year-old novice drivers have a higher accident risk than that of 17-year-olds, whose risk is similar to that of 18- and 19-year-old novices.

How long drivers have been licensed has a far bigger impact on crash risk, Dr. Johnston said (Traffic Inj. Prev. 2009 Jun;10[3]:209-19).

But the risk of an accident also increases with each additional passenger a teen driver has, particularly for younger and male drivers (Traffic Inj Prev. 2013;14[3]:283-92). More passengers likely means more distraction, and distraction, driving too fast for road conditions, and not scanning the roadway are the three most common errors – together accounting for about half of all teen drivers’ crashes.

Risk factors for accidents

Speed is a contributing factor in just over a third (36%) of teens’ fatal crashes. Adolescents drive faster and keep shorter following distances than adults do. But as with adults, wearing seat belts substantially reduces the risk of death in accidents.

Lap-shoulder seat belts reduce the risk of death in a crash by 45%, but teens use their seat belts far less often than do older drivers. Nationally, 90% of drivers use seat belts, with higher rates in states with primary enforcement (92%) than those in states with secondary enforcement (83%).

But barely more than half (54%) of U.S. high school students say they “always” wear a seat belt, and just under half of teens (47%) who died in crashes in 2017 weren’t wearing one. As seen in adults, teens are more likely to buckle up, by 12%, in states with primary seat belt laws.

Distraction during driving can be visual, manual, or cognitive – and handheld electronic devices such as smartphones cause all three distraction types. Cell phones nearly double the proportion of teen drivers who die in crashes, from 7% to 13%.

But if teens can keep their eyes on the roadway at all times, even the risks posed by cellphones drop considerably.

“The best evidence shows that secondary tasks only degrade driving performance when they require drivers to look away from the road,” Dr. Johnston said. Looking away for 2 seconds or longer increases crash risk more than fivefold.

Two other risk factors for teen car accidents are drowsiness and nighttime driving. Sleepiness can play a role in crashes at any time of day, and Dr. Johnston noted that some research has associated later high school start times with reduced crash risk.

Teens aged 16-19 years are about four times more likely to have a car accident at night than during the day per each mile driven, the pediatrician noted. Many licensing laws restrict teen driving starting at 11 p.m. or later, but about 50%-60% of their crashes occur between 9 and 11 p.m.

One reason for the increased risk is less experience driving in more difficult conditions, but teens also are more likely to have teen passengers, to be driving excessively fast, or to be under the influence of alcohol at night.

Adolescents’ crash risk is higher than that of adults for any level of blood alcohol content. Self-reported driving after drinking dropped by almost half – from 10% to 5.5% – from 2013 to 2017, but alcohol still is implicated in a substantial number of fatal teen crashes.

As drunk driving has declined, however, driving while under the influence of marijuana has been increasing. According to the National Highway Traffic Safety Administration, case control studies show drivers with tetrahydrocannabinol (THC) in their blood have a 25% increased risk of accidents – but the excess risk associated with THC vanishes when researchers control for age, sex, and concurrent use of alcohol. Not enough research exists to determine what the crash risk would be for adolescent drivers using THC alone.

A less-recognized risk factor for car accidents in teen drivers is ADHD, which increases a teen’s risk of crashing by 36%, particularly in the first month after getting a license, Dr. Johnston said.

ADHD medication appears to mitigate the danger, according to data: Crash risk was 40% lower in adult drivers with ADHD during months they filled their stimulant prescriptions. But one study found only 12% of teens with ADHD filled their prescriptions the month they got their license, and adolescents may not take their medications or still have them in their system on weekends or at night.

Teens recovering from concussion also may have an increased risk. Some evidence suggests driving impairment continues even when other symptoms have resolved, but not enough data exist to determine appropriate criteria for clearing teens to begin driving again.

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