Abstract: The visual load of a driver changes significantly while driving through the entrance and exit sections of a highway tunnel. To quantify the change law of the visual load at these sections, 10 drivers are selected for conducting a driving test at the ZhashuitoXi′an section of Zhongnanshan highway tunnel in Qinling Mountains. Data such as illuminance, vehicle speed, and pupil area of the drivers passing through the tunnel entrance and exit sections on sunny days are collected. By analyzing the change characteristics of the drivers′ pupil area at the entrance and exit of the tunnel, the concept of the relative change intensity of pupil area (RCPA) is proposed. The concept is based on physical and medical parameters, such as the peaktoaverage ratio and frequency band ratio, which are as evaluation indices of the drivers′ visual load. In addition, the relationships between the indices and visual comfort are revealed. Finally, a mathematical model showing the relationships between the RCPA and velocity and illumination is established. The results reveal the following. (1) The RCPA sufficiently reflects the law of gradual accumulation and sharp flatuations of the visual load at the entrance and exit of the tunnel. (2) The instantaneous visual load of the drivers is the largest when they are about to enter or leave the tunnel, and this load exceeds the physiological limits of the drivers. (3) The quantitative relationships between the RCPA and speed and illuminance can provide a reference for setting safe speed thresholds at tunnel entrances and exits and improving the lighting environment in tunnels.

Key words: highway tunnel entrance and exit, visual load, pupil area, relative change intensity, modeling