The presence of passengers in a vehicle has been shown to increase the risk of fatal crash involvement for teenage drivers; however, the studies that have quantified this relationship were based on data that are now over a decade old. In the years since these studies, most U.S. states have enacted graduated driver licensing systems that limit the number of passengers that young drivers are allowed to carry during their first several months of independent driving, and the number of 16- and 17-year-old drivers involved in fatal crashes each year has decreased by more than half. The objective of this study was to provide updated estimates of the relationship between the number and ages of passengers present and the crash risk per mile driven of 16- and 17-year-old drivers. Data on crashes that occurred in years 2007—2010 and data on the number of miles driven in years 2008—2009 were examined. Rates of crash involvement and driver death per mile driven were estimated for 16- and 17-year-old drivers with no passengers; with one, two, and three or more passengers younger than age 21 (and no older passengers); and with at least one passenger aged 35 or older. Compared with having no passengers, having one passenger younger than age 21 (and no older passengers) was associated with a 44% increase in a 16- or 17-year-old driver’s risk per mile driven of being killed in a crash (Relative Risk [RR] 1.44, 95% Confidence Interval [CI] 1.01 — 2.04). Having two passengers younger than age 21 was associated with a doubling of a driver’s risk of being killed in a crash, compared with having no passengers (RR 2.02, 95% CI 1.36 — 2.99). Having three or more passengers younger than age 21 was associated with roughly a quadrupling of a driver’s risk of being killed in a crash, compared with having no passengers (RR 4.39, 95% CI 1.45 — 13.31). The relative risk of being involved in any police-reported crash in the presence of young passengers followed a similar pattern; however, the increases in relative risk of being involved in any police-reported crash were smaller and were not statistically significant. Having at least one passenger aged 35 or older in the vehicle was associated with a 62% decrease in a 16- or 17-year-old driver’s risk per mile driven of being killed in a crash (RR 0.38, 95% CI: 0.24 — 0.60), and a 46% decrease in the risk of being involved in any police-reported crash (RR 0.54, 95% CI 0.35 — 0.84), compared with having no passengers. These results show that although the overall number of teen driver fatalities has decreased substantially over the past several years, carrying young passengers is still a significant risk factor for young drivers. In contrast, carrying adult passengers significantly reduces the risks of crash involvement. (Author/publisher)
Samenvatting