The effects of tunnel radius, turn direction, and zone characteristics on drivers’ visual performance

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This study aimed to explore the influence of the tunnel radius, turn direction, and zone characteristics on drivers’ visual performance. The study used a field experiment, in which 30 participants drove real vehicles in different curved tunnels, and measured their fixation duration (FD), fixation frequency (FF), saccade duration (SD), and saccade amplitude (SA) as indicators of visual performance. The results showed that the tunnel radius, turn direction, and zone characteristics had significant effects on all four indicators of visual performance. As the tunnel radius decreases, drivers exhibit longer FD and larger SA, while FF and SD decrease correspondingly. Additionally, the directional aspect of turning significantly influences these eye movement parameters, with drivers demonstrating longer FD, lower FF, shorter SD, and smaller SA during left turns compared to right turns. Irrespective of turning direction, drivers allocate the longest average FD and highest FF in the entrance zone, followed by the middle zone, and the shortest duration in the exit zone under the same tunnel radius condition. Similarly, the mean SD and amplitude are highest in the exit zone, followed by the middle zone, and lowest in the entrance zone, regardless of the turning condition. These findings suggest that drivers adjust their visual behavior according to the dynamic and complex visual stimuli and the varying driving task demands in different scenarios of curved tunnel driving. These findings also imply that drivers face different perceptual and cognitive challenges and preferences when driving in curved tunnels with different radii, turn directions, and zone characteristics, which affect their visual adaptation and preparation processes, as well as their visual integration and differentiation processes. This study has some implications and suggestions for the design and management of curved tunnels, as well as for the education and training of drivers. This study also provides new theoretical and empirical evidence for the visual behavior and cognition of drivers in curved tunnels, and provides practical suggestions for enhancing their visual performance and improving their driving safety and efficiency in curved tunnels.