Date of Award

January 2013

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)



First Advisor

Federico E. Vaca

Subject Area(s)

Medicine, Epidemiology, Public health


Background: Despite recent prevention gains, motor vehicle crashes continue to be the leading cause of death for US adolescents and young adults. Many of these deaths involve young unlicensed drivers that are more likely to be in fatal crashes and to engage in high-risk driving behaviors like impaired driving, speeding, and driving unrestrained. In a crash context, the influence of these high-risk behaviors may spillover to adversely affect passenger safety restraint use. Objective: To examine the effect of young unlicensed drivers on safety restraint use and mortality of their passengers. Methods. A cross-sectional analysis of the National Highway Traffic Safety Administration's Fatality Analysis Reporting System from years 1996-2008 was conducted. Fatal crashes involving unlicensed drivers (15-24 yrs) and their passengers (15-24 yrs) were included. Multivariate logistic regression with generalized estimating equations were undertaken to assess the relationship between unlicensed driving and passenger restraint use, controlling for established predictors of restraint use, including driver restraint use, passenger gender, alcohol use, number of occupants, crash year, and crash location (rural vs. urban). Results: 102,092 passengers were involved in fatal crashes nationally from 1996-2008 with 64,803 unique drivers. 6,732 (10.51%) were never licensed drivers and 5,603(8.8%) were drivers with suspended, revoked, or expired licenses. Rates of unlicensed driving ranged from 17.7% to 25.1% and increased over time. While passengers in fatal crashes averaged 40.9% restraint use, passengers of never and invalidly licensed drivers had a further decreased odds of wearing a safety restraint (OR 0.73, 95% CI 0.69-0.77, p<0.001) and (OR 0.84, 95% CI 0.79-0.90, p<0.001). Other factors related to passenger restraint use were driver restraint use (OR 15.40, 95% CI 14.71-16.11, p<0.001), being a front- seated passenger (OR 3.61, 95% CI 3.47-3.74, p<0.001), rural crash location (OR 0.71, 95% CI 0.68-0.74, p<0.001), and driver alcohol use (OR 0.74, 95% CI 0.70-0.77, p<0.001). Conclusions: We found a strong inverse correlation between unlicensed driving and passenger restraint use, suggesting a significant risk spillover effect. Unlicensed driving was involved in a disproportionate and increasing number of fatal crashes and plays a detrimental role in the lifesaving safety behaviors of their passengers. Unlicensed driving not only puts the driver and public at risk, but may also diminish passengers' ability to mitigate risk in a crash context. Our findings highlight an alarming peer influence between unlicensed drivers and passengers that has considerable implications for US highway safety and the public's health. Further in-depth study in this area can guide the development of targeted countermeasures and traffic safety programs.


This is an Open Access Thesis.

Open Access

This Article is Open Access