Visual characteristics of drivers in different directions and lengths of gradual landscape zones in extra-long highway tunnels

Owing to the tightness and monotonicity of the tunnels, the number of traffic accidents caused by driving through them for a long time is positively correlated to their length. To improve driving safety, a landscape zone with the function of awakening the driver and relieving their fatigue has been adopted in an increasing number of extra-long highway tunnels. However, the sharp contrast between the landscape and ordinary zones often makes drivers uncomfortable. Therefore, a gradual landscape zone is proposed in this study. Through driving simulation tests, the eye movement and pupil index were used to study the attractiveness, direction, and length of the gradual landscape zone in an extra-long highway tunnel. The results show that there is no risk of causing excessive distraction to drivers in the "blue sky and white clouds" landscape zone of the tunnel vault, and the gradual landscape zone in the approach direction has a significant influence on the change rate of the pupil diameter range of drivers. In contrast, the gradual landscape zone in the driving direction has little influence. For a longer length of the gradual landscape zone in the approach direction, drivers require a longer adaptation time at the descent stage of the pupil diameter, and the change rate of the pupil diameter range is smaller. Therefore, a longer gradual zone in the approach direction is helpful in improving the adaptability of drivers when passing through the landscape zone.