Safety Effects of an Improved Highway Tunnel Lighting Environment: A Real-Vehicle Study of Drivers’ Visual and Physiological Responses

Abrupt changes in the lighting environment at highway tunnel entrances, transition zones, and exits can impose substantial visual adaptation demands on drivers. This real-vehicle study evaluated a modified LED tunnel lighting environment designed to enlarge the effective luminous area, improve road surface lighting uniformity, and reduce direct glare, compared with the original lighting system. The field experiment was conducted using 24 licensed drivers in a 610 m highway tunnel. Pupil area, mean fixation duration, and heart rate growth rate (HRG) were recorded in six longitudinal zones under the original and modified lighting conditions. The measured interior zone illuminance uniformity increased from 0.71 to 0.87 after modification. Repeated-measures ANOVA showed significant lighting-by-zone interactions for all three outcomes (p ≤ 0.001). Bonferroni-adjusted comparisons localized significant reductions in pupil area and HRG in the threshold, transition, and interior zones, while fixation duration increased significantly in those zones and in the exit zone. Across the averages for the six zones, pupil area decreased by 8.39%, HRG decreased by 13.78%, and mean fixation duration increased by 6.63%. The findings suggest that the modified lighting environment reduced visual adaptation demand and physiological arousal, especially in the threshold and transition zones. Fixation duration changes are interpreted as altered visual information processing rather than direct evidence of improved safety, and no inference about crash reduction can be made without direct driving performance or safety outcome data.