Unpacking older drivers' mobility at roundabouts: Their visual-motor coordination through driver-vehicle-environment interactions

While mobility and safety of older drivers are challenged by age-related cognitive changes, the increasingly complex road environment has placed a higher demand on their adaptability. Older drivers experience difficulties in regulating their operational level behaviors which rely on the second-to-second decision-making, e.g., using the visuospatial information to guide their steering. The roundabout maneuver is one of the critical scenarios for older drivers which requires efficient visual and motor coordination. Understanding older drivers' visual-motor coordination at roundabouts will provide insights into the mobility and safety of older driver population, which is important yet to be explored. This paper contributes to new measurements in driving behavior through quantitative examinations on driver-vehicle-environment interactions. The drivers' visual-motor coordination is conceptualized as a sequence of eye fixations coupling with the vehicle trajectory in a space-time path. The experimental data were from 38 older adults' on-road driving recorded using context and location-aware enabled eye tracking and precise vehicle movement tracking. A visual-motor coordination composite indicator (VMCCI) was developed to measure the efficiency of visual-motor coordination in GIS based on the aggregate multiple parameters of visual and motor behaviors at entry, circulating and exit stage of a roundabout. The results show that the VMCCI is a sensitive indicator for identifying risky drivers, problematic road sections, problematic behaviors. Older drivers' VMCCI was associated with the angle of deviation at roundabouts, particularly at the entry stage. Findings of this study have implications for actual roundabout designing practice, which will contribute to improve the safety of older drivers behind the wheel