Cognitively impaired older drivers are less likely to cause a crash when accompanied by a passenger

Tsukuba, Japan—To reduce traffic crashes involving older drivers, driving lessons and cognitive assessments have long been part of driver's license renewal processes. Recently, efforts have expanded to include promoting vehicles equipped with advanced driver assistance technologies. In this study, the researchers built upon findings from studies conducted outside Japan, which indicated that older drivers are less likely to be involved in crashes when accompanied by a passenger. Additionally, some countries have implemented conditional licensing systems that require older drivers to have a passenger in their car. The researchers hypothesized that even among drivers with impaired cognitive function, the risk of causing a crash would be lower when accompanied by a passenger.

This study focused on license holders aged 75 years and older who underwent cognitive assessments and renewed their licenses between 2014 and 2017. Among these drivers, those involved in car-to-car crashes during the three years after their license renewal were classified as either first party (at-fault) or second party (not-at-fault). The researchers then compared the presence of a passenger at the time of the crash based on cognitive assessment results, including those identified as having suspected dementia. Passenger presence was also analyzed by gender.

The analysis revealed that, regardless of cognitive functions, second-party drivers were more likely to have been accompanied by a passenger than first-party drivers, for both male and female participants. However, no significant differences were found in other factors potentially contributing to crash occurrence, such as age, prior crash history, or the time, weather, and location of the crash.

These results suggest that older drivers, even those flagged for potential cognitive decline or suspected dementia during assessments, may have a reduced likelihood of being the first party in car-to-car crashes if accompanied by a passenger. While the results do not establish causality, they highlight the potential role of passengers in promoting safer driving among older drivers.

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This work was supported by JSPS KAKENHI (Grant Number 21H03195).

_{Original Paper}

Title of original paper:
Association between the presence of passengers and at-fault crash risk among cognitively impaired older drivers

Journal:
Journal of Safety Research

DOI:
10.1016/j.jsr.2025.04.002

Professor ICHIKAWA, Masao
Institute of Medicine, University of Tsukuba

Associate Professor INADA, Haruhiko
Department of Public Health and Health Policy, Graduate School of Medicine, The University of Tokyo

Dr. KOSUGE, Hanae
Senior Researcher of the Institute for Traffic Accident Research and Data Analysis

Institute of Medicine

Journal of Safety Research

10.1016/j.jsr.2025.04.002

Association between the presence of passengers and at-fault crash risk among older drivers with and without cognitive decline

10-Apr-2025