Effects of traffic sign information density on drivers' visual comfort in mountainous two-lane highway: A on-road driving test.

OBJECTIVE: To investigate the effects of traffic sign information density on drivers' visual comfort and visual psycho-physiological load on mountainous two-lane highways, establish their quantitative relationship, and propose a reasonable information density range based on visual comfort to support the optimized deployment of traffic signs. METHODS: On-road driving tests were conducted on the mountainous two-lane highway section with 27 drivers across 25 typical sections. Data on pupil area change rate, fixation intensity, heart rate change rate, and heart rate variability were collected. An information density model of traffic signs was developed based on information entropy theory, and factor analysis was used to establish its quantitative relationship with drivers' visual psycho-physiological load. RESULTS: Traffic sign information density was significantly positively correlated with pupil area change rate, fixation intensity, and heart rate change rate, but negatively correlated with heart rate variability. A significant quantitative relationship was identified between information density and visual psycho-physiological load, with the quadratic regression model providing the best fit and an adjusted R2 of 0.754. Based on visual comfort classification, information density could be divided into five levels. CONCLUSIONS: Traffic sign information density on mountainous two-lane highways significantly affects drivers' visual search behavior, psycho-physiological load, and visual comfort, with a relatively stable functional relationship between them. From the perspective of visual comfort, the information density is recommended to remain below 0.373 bits/m and should not exceed 0.507 bits/m. These findings provide a quantitative basis for the rational deployment and optimal design of traffic signs on mountainous two-lane highways.