Published December 8, 2025

Together, two new University of Iowa studies shed light on road safety, one examining teenage drivers and passengers, and the other focusing on drivers across a broader range of ages.

One study, published in the Journal of Safety Research, looked at the impact of teen perceptions of parental monitoring on risky driving behaviors of teen drivers, such as texting while driving or driving after drinking alcohol, and risky passenger behaviors like not wearing a seat belt or riding with a driver who has been drinking.

The second study, published in Traffic Injury Prevention, explored how having passengers in the vehicle affected a driver’s likelihood of being at fault for a crash and how this varied by age, ranging from 14 to over 75 years.

Key findings: Teens who perceived high parental monitoring engaged in fewer risky driving and passenger behaviors. Additionally, having passengers in the vehicle was associated with drivers being less likely to be at fault in a failure-to-yield crash; however, this effect was observed only among drivers aged 45 and older.

Teen driving & parental monitoring

Amir Ghanbari, PhD candidate in the Department of Epidemiology, led the study published in the Journal of Safety Research, which found that greater perceived  parental monitoring was associated with less risky teen driving. He analyzed data from the 2021 National Youth Risk Behavior Survey, a national survey of high school students in grades 9 – 12. 

“We defined parental monitoring based on teens’ own perceptions of how often their parents or caregivers know where they are and who they are with,” he said. “This reflects a basic level of communication and awareness between parents and teens.”

What stood out in this study, Ghanbari said, was that even basic parental monitoring significantly reduced reported risky road behaviors for both drivers and passengers.

“Seeing such a strong effect from a single, simple measure highlights how powerful even minimal communication and awareness can be,” he said.

The study also found that male teenagers were more likely than females to engage in risky driving behaviors (7.1% vs. 4.2%). However, the percentages of males and females reporting risky passenger behaviors were similar (5.0% vs. 5.5%).

In addition, as teens got older, risky passenger behaviors increased, from 5% among those 15 and younger to 8.6% at age 18. Similarly, risky driver behaviors rose with age (2.6% to 8.8%, respectively).

Ghanbari said parents can set clear expectations, regularly check in about their teens’ whereabouts, and discuss safe driving rules like avoiding distractions and never riding with an impaired driver.

“Maintaining open communication and staying involved, even informally, can make a meaningful difference,” he said. “Research consistently shows that teens who feel monitored take fewer risks on the road.”

The study also found that teens who reported sleeping in public places were more likely to engage in risky driving behaviors. Where teens sleep can reflect the stability of their environment, Ghanbari said, as well as the level of supervision they experience.

“Based on our definition of parental monitoring, some might assume that teens living with their parents automatically have higher monitoring. To account for this, we adjusted for sleep place in our analysis,” he said.

Passenger presence and driver age

Gilsu Pae, a former postdoctoral scholar in the Department of Epidemiology, led the study published in Traffic Injury Prevention. It found that that having a front-seat passenger was associated with fewer failure-to-yield driving errors for drivers aged 45 and older, with the strongest effect observed among those aged 45-65.

This association was not seen in younger drivers, aged 14-44. The study noted possible explanations such as driver inexperience and a lack of help from passengers, who may be young, sleeping, or using mobile phones.

Drivers most likely to be at fault in failure-to-yield crashes when passengers were present were the youngest and older age groups (14-24 and 65+ years).

Pae said passengers can distract young, inexperienced drivers during critical moments on the road. Older drivers can benefit from having passengers, he said; however, this advantage cannot fully offset the risks related to age-related declines in physical and cognitive abilities.

“Additionally, older drivers are often accompanied by older passengers who may also experience similar declines, and therefore, provide limited assistance,” Pae said.

The presence of a front-seat passenger was associated with fewer failure-to-yield driving errors compared to the presence of rear-seat passengers. The study noted that this suggests front-seat passengers share a common awareness and may assist drivers by alerting them to their surroundings.

The research team analyzed data from the Iowa Department of Transportation related to failure-to-yield crashes from 2015 to 2020. The analysis included only collisions involving more than one vehicle where a single driver was identified as at fault. Most (98%) were two-vehicle crashes.

“We focused on failure-to-yield crashes because they often occur in complex driving situations where passenger assistance or distraction can significantly influence driver behavior and safety,” Pae said.

Pae said he was interested in examining how passengers can assist drivers of various ages, considering declines in driving abilities related to age or lack of driving experience.

“The findings indicate the potential for future vehicle safety technologies to provide similar support,” he said.

Other UI IPRC resources:

Hands-free law goes into effect in Iowa

Older driver crash injuries and licensing renewal

Car crashes: When teens are at fault

Preventing impaired driving among youth

Keeping teen drivers and roads safer (policy brief)