Why Does Driver Attention Abnormally Decrease? − an Experimental Analysis on the Slack Effect at Highway Tunnel Entrances and Exits

This study explores the slack effect of highway tunnel entrances and exits and analyses its impact on traffic safety. Forty-five drivers were recruited to conduct vehicle experiments and to collect eye movement data while driving in highway tunnels. Analyze the variation patterns of various indicators in different areas of the tunnel, and explore the relationships among the light environment, visual adaptation, visual search and attention distribution. The study shows that at the tunnel exit during the day and at the tunnel entrance at night, the illuminance changes dramatically and the white-hole effect occurs. In the area affected by the white-hole effect, the risk of accidents is high, but the fixation frequency in the safety gaze areas (PSGA) is low, and the driver’s attention is abnormally reduced. When the traffic environment transitions from poor to good, there is a slack effect due to optimistic psychological expectations, where drivers are psychologically relaxed and tend to ignore driving risks. Compared to open roads (during the day), tunnels are dim and enclosed, with a higher driving load and a negative driving attitude. When the driver sees the tunnel exit, they feel relaxed due to the slack effect, which triggers abnormal phenomena such as abnormal decrease in attention and abnormal acceleration. Similarly, the traffic environment at the tunnel entrance at night transitions from poor to good, and there is also a certain degree of slack effect. There is a concomitant phenomenon of slack effect and white hole effect, and the combination of abnormal decrease in attention (slack effect) and visual interference (white-hole effect) can seriously threaten tunnel traffic safety.