Investigation on the impact of visual guidance facilities in the middle section of expressway tunnels on drivers' visual characteristics

To comprehensively examine how visual guidance installations within expressway tunnel mid-sections affect drivers' visual behavior, this investigation deliberately prioritized the tunnel's central segment as the core analytical zone. Our experimental design featured two contrasting conditions: a baseline configuration completely lacking visual guidance elements, and an intervention configuration incorporating a multi-component guidance system—comprising raised pavement markers, retroreflective delineators, tunnel wall rings, and continuous waistline markings. Thirty licensed drivers participated in real-world driving trials at Yunling Tunnel, where ocular metrics were recorded via eye-tracking apparatus. Pupillary diameter fluctuations and gaze distribution patterns functioned as primary visual characteristic indicators. We employed the LOWESS (Locally Weighted Scatterplot Smoothing) technique for data preprocessing to mitigate anomalous data incidence. Subsequent analytical procedures then examined trial outcomes. The evidence indicates that during mid-tunnel transit, operators' psychological stress exhibits a progressive reduction before stabilizing, while their predominant attentional focus remains oriented toward the forward roadway. Critically, tunnel mid-section visual guidance infrastructure demonstrates capacity to further diminish drivers' psychological load. These installations effectively engage operator attention, preventing excessive fixation on the immediate path ahead, which in turn appears to enhance driving comfort. Ultimately, this research offers new insights into the operational mechanisms through which visual guidance infrastructure modulates drivers' visual processing, while also establishing empirical support for optimizing tunnel-based guidance system evaluations. By delineating actionable strategies for leveraging visual guidance to advance tunnel safety and comfort parameters, our findings carry meaningful implications for future expressway tunnel management frameworks.