How do driving speed and luminance change rate affect driving visual comfort? A field vehicle test on mountain highway tunnels

OBJECTIVE: This study aims to investigate the factors influencing drivers' visual-psychological comfort at the tunnel portal sections of two-lane mountainous highways, as well as the mechanism by which the environmental conditions at these sections affect drivers' visual-psychological comfort. The findings are intended to provide a theoretical basis for the safety design and traffic management of tunnel portal sections. METHODS: Data were collected through field vehicle tests. The Principal Component Analysis (PCA) was employed to fuze the driving visual and psychological indicators. The K-means clustering algorithm was adopted to classify comfort levels into three categories: "Comfortable", "Relatively Comfortable", and "Uncomfortable". The ordered logistic regression method was utilized to analyze the impacts of eight variables on comfort levels. Furthermore, the decision tree model was applied to identify the key nodes and threshold values of indicators that lead to the differences in comfort levels. RESULTS: Driving experience, driving speed, luminance change rate, and driver temperament type exert a significant influence on visual-psychological comfort, among which driving speed is the dominant factor and luminance change rate is the secondary factor. A driving speed of 47 km/h acts as the threshold differentiating the "comfortable" and "relatively comfortable" states, whereas 53 km/h marks the threshold between "relatively comfortable" and "uncomfortable". Similarly, a luminance change rate of 8.5% is the threshold for distinguishing "comfortable" from "relatively comfortable", and 28.5% is the threshold separating "relatively comfortable" from "uncomfortable". CONCLUSIONS: Driving speed and luminance change rate are the two most critical controllable environmental factors that affect driving visual psychological comfort. The study results offer specific quantitative thresholds for speed limit setting and lighting transition design of these road sections, which may help enhance driving safety and improve driving experience.