## 4 Discussion
### Analysis of Time-Varying Characteristics of Glare in the Access Zone of West Oriented Tunnel  
An analysis was conducted on the time-varying characteristics of glare in the access zone of a west oriented tunnel, as shown in Figures 16 and 17. From Figures 16 and 17, the glare value of the tunnel facing west generally shows an increasing trend followed by a decreasing trend, with a higher glare value in the afternoon compared to other time periods. Uncomfortable and intolerable glare appeared from 15:00 p.m. to 16:00 p.m., which was caused by the difference in luminance inside and outside the tunnel. The luminance of the Youyi Tunnel from 15:00 p.m. to 16:00 p.m. is too large, reaching 1.03 and 1.79 times of the recommended value of the \"Guidelines for Design of Lighting of Highway Tunnels\", respectively, which is unreasonable. At this time, the _PGSV_ values were 2.91 and 3.22, respectively, reaching the intolerable glare value limit. Currently, the corresponding luminance difference outside the tunnel is about 95% and 97%, which occurs at the moment when the luminance difference inside and outside the tunnel is the largest in a day. The overall trend of the L\({}_{20}\)(S) is to increase first and then decrease, and the maximum value appears from 14:00 p.m. to 16:00 p.m. At the same time, the overall change trend of the luminance difference degree inside and outside the tunnel due west is also to increase first and then decrease. Therefore, the time-varying characteristics of glare are roughly the same as the L\({}_{20}\)(S) value and the difference degree of luminance inside and outside the tunnel. So, when the tunnel entrance and the surroundings are directly exposed to sunlight, the luminance outside the tunnel increases. Since the luminance inside the tunnel  
Figure 15: _PGSV_ for the east gate of the Tiangongtang Tunnel. is always maintained in a very low state, and the luminance difference between inside and outside the tunnel is large, this leads to the phenomenon of improper luminance in the visual environment at the access zone of an east-west oriented road tunnel, resulting in uncomfortable glare and disabling glare at the access zone, which will seriously affect driving safety and comfort. As can be seen from Figures 13-17, the luminance difference between the inside and outside of the Tongmao tunnel is less than 82%, and the luminance inside the tunnel is higher than that of other tunnels. Therefore, there was almost no uncomfortable or even intolerable glare phenomenon in the Tongmao tunnel during the test. There is an indirect uncomfortable glare phenomenon caused by the difference of luminance inside and outside the tunnel due to the excessive luminance outside the tunnel. Therefore, the influence of the uncomfortable glare on the visual environment of the tunnel should be considered in the lighting design of the road tunnel with the direction of east to west. At the same time, the adverse effects of glare in the access zone should be considered in the design of luminance and surroundings outside the tunnel to improve the driver's driving safety and comfort. Analysis of Time-Varying Characteristics of Glare after Rainfall in the Access Zone of West Oriented Tunnel  
Generally, during or after rainfall, the luminance outside the tunnel will decrease due to weather conditions. However, after rainfall, the scenery outside the tunnel and the surface of the road surface can readily form indirect glare sources when combined with water, thus directly affecting the driver's glare. Therefore, considering the actual situation of driving after rainfall, the glare problem in the tunnel conditions after rain was analyzed, and the results are shown in Figure 18.  
Figure 16: PGSV for the west portal of the Youyi Tunnel. Figure 17: \(PGSV\) for the west portal of the Tongmao Tunnel. During the test of Longquanshan No. 1 Tunnel, rain occurred during 10:00-12:00 a.m. and 16:00 p.m., respectively. The surroundings in the access zone and the road surface were wet and there was a reflective phenomenon.