Li-Hui Chen, PhD, from the Johns Hopkins University School of Hygiene and Public Health, Baltimore, and colleagues studied data from the Fatality Analysis Reporting System and General Estimates System (1992-1997), and from the Nationwide Personal Transportation Survey (1995).
They discovered that compared with drivers of the same age without passengers, the relative risk of driver death per 10 million trips was 39 percent higher for 16-year-old drivers with one passenger, 86 percent higher for those with two passengers, and 2.82 times higher for those with three or more passengers. The estimated overall death rate for 16-year-old drivers per 10 million trips was 1.99 with 0 passengers, 2.76 with one passenger, 3.69 with two passengers, and 5.61 with three or more passengers. Similar patterns of increasing death rates and increasing relative risks of death with increasing numbers of passengers were noted for 17-year-old drivers.
The risk of death increased significantly for drivers transporting passengers irrespective of the time of day or sex of the driver, although male drivers were at greater risk. Driver deaths per 1,000 crashes increased for 16- and 17-year-olds transporting male passengers or passengers younger than 30 years. In contrast, 30-to 59-year-old drivers who carried passengers had decreased death rates. The authors also noted that the death rates for teen drivers were substantially increased between 10 p.m. and midnight, and between midnight and 6 a.m., compared to daytime driving.
The researchers' study showed that passengers aged 20 to 29 in cars with 16- and 17-year-old drivers increased the likelihood of fatal outcomes when these drivers crashed. They write that this finding suggests a restriction on carrying any teenagers unless supervised by an adult at least 21 years old could have a negative effect if it increased the transport of passengers aged 20 to 29.
"Why were there more deaths when 16- and 17-year old drivers carried passengers?" the researchers write. "A survey [a previous study] of 192 high school drivers reported that dangerous driving behaviors (driving after drinking alcohol or using drugs, speeding, swerving, crossing the center line, purposely skidding, and running a red light) were strongly associated with the presence of peers."
The authors recommend use of a graduated licensing system for teens. "The basic premise of these systems," they write, "is that beginning drivers need to earn a full license step-by-step. Three stages - a supervised learner's permit, an intermediate license, and a full-privilege driver's license - are the central framework for graduated licensing systems. During the learner's period, beginning drivers can drive only under supervision. For the intermediate period, restrictions vary widely by state in the United States and may include restrictions on nighttime driving and carrying passengers."
They explain that as of January 2000, 24 states had adopted full graduated licensing systems with all three stages. Only nine of these 24 states included any restrictions related to teenaged drivers carrying passengers.
The authors add that motor vehicle crashes are the leading cause of death among teenagers in the United States, accounting for 36 percent of all deaths of persons aged 15 to 19 years and that the fatal crash rate per million miles for 16-year-old drivers is more than seven times the rate for drivers aged 30 to 59 years. Nearly the same number of deaths occur among teenaged passengers as teenaged drivers: in 1993, two thirds of the deaths of passengers aged 13 to 19 years occurred when teenagers were driving.
This work was supported by the Insurance Institute for Highway Safety and by a grant from the Centers for Disease Control and Prevention to the Johns Hopkins Center for Injury Research and Policy.
(Journal of the American Medical Association. 2000; 283:1578-1582)
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