An Empirical Study on the Impact of Information Content of Traffic Signs in Entrance Areas of Highway Tunnels on Drivers' Visual Behavior

To evaluate the impact of information content of traffic signs in entrance areas of highway tunnels on drivers' visual behavior, this study conducted a real-driving experiment, combined with eye movement entropy and a coupling coordination degree model, with which the influence patterns of different levels of information content on drivers' visual behaviors is explored and the coordination mechanism between information content and characteristics of eye movement is revealed. The experiment selected six entrance areas of highway tunnels, representing six levels of information content of traffic signs (i.e., T0—T5, ranging from 0 to 81.18 bits). Forty drivers were recruited wearing eye trackers to collect eye movement data. Metrics such as fixation duration, saccade duration, and saccade amplitude were analyzed. Eye movement entropy was calculated based on sample entropy theory to analyze the complexity of visual search patterns, and a coupling coordination degree model was constructed to assess the coordination level between information content and eye movement behavior. The results indicated that the information content of traffic signs in the entrance areas of highway tunnels significantly affected drivers' eye movement characteristics. As the information content increased, fixation and saccade durations first decreased and then increased, while saccade amplitude first increased and then decreased. The T3 level (i.e., 48.31 bits) showed the best performance across all metrics, reflecting the highest efficiency in drivers' information perception and search. As vehicles approached the tunnel, the sample entropies of fixation duration, saccade duration, and saccade amplitude all gradually increased, and the rate of growth within the recognition sight distance range (125—100 m) significantly increased, indicating that drivers' search intensity for environmental information increased as the distance shortened. At the T3 level, eye movement entropy was the smallest, and the visual search pattern was the most stable. The coupling coordination degree between information content and eye movement behavior exhibited a unimodal curve that first increased and then decreased. The coupling coordination degree at the T3 level reached 0.851, which falls in a "good coordination" level (Level 9), while both levels of insufficient information (T0—T1) and information overload (T4—T5) resulted in a state of imbalance.