The Iowa graduated driver licensing program: Effectiveness in reducing crashes of teenage drivers

David M. Neyens, Birsen Donmez, Linda Ng Boyle

Research output: Contribution to journalArticlepeer-review


Problem: Graduated Driver Licensing (GDL) programs vary in the United States in terms of implementation and restrictions. The State of Iowa's GDL program is assessed for its effectiveness in reducing crashes among teenage drivers. Method: Time series analysis was used to evaluate police documented crashes involving 16-, 17-, and 18-year-old drivers over a 10 year period, with an intervention identified at the point of GDL implementation. Results: After controlling for seasonal trends and auto-correlative effects, a significant reduction in the crash rate of and 16- and 17-year-old drivers was observed due to the GDL implementation. However, there were no significant reductions in crash rates for 18-year-old drivers. Discussion: The analyses suggest that the Iowa GDL program is effective in reducing the crash rates of 16- and 17-year-old drivers but the effects do not sustain for 18-year-old drivers. Impact on Industry: The results suggest that the program appears to be working, however further analysis is needed to determine what factors are preventing lasting effects for these teenage drivers.

Original languageEnglish (US)
Pages (from-to)383-390
Number of pages8
JournalJournal of Safety Research
Issue number4
StatePublished - 2008


  • ARIMA model
  • crash rates
  • intervention analysis
  • Teenagers
  • time-series analysis
  • young drivers

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality


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