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The association of graduated driver licensing with miles driven and fatal crash rates per miles driven among adolescents
  1. Motao Zhu1,2,
  2. Peter Cummings3,
  3. Songzhu Zhao2,
  4. Jeffrey H Coben2,4,
  5. Gordon S Smith5
  1. 1Department of Epidemiology, West Virginia University, Morgantown, West Virginia, USA
  2. 2Injury Control Research Center, West Virginia University, Morgantown, West Virginia, USA
  3. 3School of Public Health and Harborview injury Prevention & Research Center, University of Washington, Seattle, Washington, USA
  4. 4Department of Emergency Medicine, West Virginia University, Morgantown, West Virginia, USA
  5. 5Department of Epidemiology and Public Health, School of Medicine, University of Maryland, Baltimore, Maryland, USA
  1. Correspondence to Dr Motao Zhu, Department of Epidemiology and Injury Control Research Center, West Virginia University, PO Box 9151, Morgantown, WV 26506, USA; mozhu{at}hsc.wvu.edu

Abstract

Background Graduated driver licensing (GDL) laws are associated with reduced crash rates per person-year among adolescents. It is unknown whether adolescents crash less per miles driven or drive less under GDL policies.

Methods We used data from the US National Household Travel Survey and Fatality Analysis Reporting System for 1995–1996, 2001–2002 and 2008–2009. We compared adolescents subject to GDL laws with those not by estimating adjusted IRRs for being a driver in a crash with a death per person-year (aIRRpy) and per miles driven (aIRRm), and adjusted miles driven ratios (aMR) controlling for changes in rates over time.

Results Comparing persons subject to GDL policies with those not, 16 year olds had fewer fatal crashes per person-year (aIRRpy 0.63, 95% CI 0.47 to 0.91), drove fewer miles (aMR 0.79, 95% CI 0.63 to 0.98) and had lower crash rates per miles driven (aIRRm 0.83, 95% CI 0.65 to 1.06). For age 17, the aIRRpy was 0.83 (95% CI 0.60 to 1.17), the aMR 0.80 (95% CI 0.63 to 1.03) and the aIRRm 1.03 (95% CI 0.80 to 1.35). For age 18, the aIRRpy was 0.93 (95% CI 0.72 to 1.19), the aMR 0.92 (95% CI 0.77 to 1.09) and the aIRRm 1.01 (95% CI 0.84 to 1.23).

Conclusions If these associations are causal, GDL laws reduced crashes per person-year by about one-third among 16 year olds; half the reduction was due to fewer crashes per miles driven and half to less driving. For ages 17 and 18, there was no evidence of reduced crash rates per miles driven.

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