Driving exposure and crash incidence density as determinants of fatal crash rates among teenage drivers

Background

Traffic crashes accounted for 40% of deaths among 16-18 year olds in 2007. Graduated Driver Licensing (GDL) delays licensure and reduces driving among adolescents aged 16-17 years, and allow them to gain driving experience under incremental risk conditions.

Methods

Using the decomposition methodology, we assessed the relative contributions of driving exposure (miles driven) and fatal crash incidence density (rate per miles driven) to population-based fatal crash rate (rate per person-years) for ages 16-17 (regulated by GDL) and 18 (beyond GDL regulation) when compared with 25-54 year olds. Data sources included the 2008 Fatality Analysis Reporting System for fatal crashes, National Household Travel Survey for miles driven, and resident population estimates.

Results

Relative to ages 25-54 years, the ratio of population-based fatal crash rates was 0.82, 1.31, and 1.84 for ages 16, 17, and 18, respectively. Compared with persons aged 25-54 years, the ratio of average annual miles driven was 0.13, 0.30, and 0.67 for ages 16, 17, and 18; the ratio of fatal crash incidence density was 6.4, 4.3, and 2.8 for ages 16, 17, and 18, respectively. The relative contribution of driving exposure to the difference in fatal crash rates was approximately 50% for ages 16-17, and 28% for age 18.

Conclusions

For 16 and 17 year olds, reduced driving offset their high fatal crash incidence density, making their fatal crash rates comparable to that for ages 25-54. For 18 year olds, increases in driving outpace the reduction in crash incidence density, thus heightening their fatal crash rate.