The moderating effect of passenger presence on the relationship between driver age and crash culpability: The co-driving influence of passengers

Passenger presence influences driver behavior and safety, with its effects shaped by the situational awareness shared between drivers and passengers. This awareness depends on factors such as driving experience and cognitive and physical abilities, which vary across age groups. However, little research has investigated how passenger presence moderates the relationship between driver age and crash culpability. This study examines the relationship between driver age and crash culpability, focusing on the moderating effect of passenger presence. This study analyzed crash data from the Iowa Department of Transportation from 2015 to 2020, focusing on drivers involved in failure-to-yield crashes (<i>N</i> = 36,577). The analytic sample was limited to multiple-vehicle collisions where the crash report indicated only one driver contributed to the crash. A multivariable logistic regression model was built to examine predictors of culpability among drivers involved in failure-to-yield crashes, with a focus on passenger presence and its interaction with driver age group. Passenger presence was significantly associated with a reduced probability of drivers being culpable in failure-to-yield crashes, with front-seat passengers having a significant effect for middle- and older-aged driver groups. The association was not significant for drivers aged 14–44 but attained significance for those aged 45 and older. Middle-aged drivers (45–64), who may begin to experience age-related declines in driving ability, benefited the most from front-seat passenger presence. The oldest drivers (75+) had a substantially higher probability of being culpable without passengers compared to the youngest drivers (14–24), whereas their probability was similar to that of the youngest drivers when accompanied by passengers. The meaningful differences in the probability of drivers being culpable between presence and absence of front-seat passengers highlight the potential of passengers as co-drivers for safe driving, offering insights for developing effective road safety interventions.