## 1 Introduction
established a quantitative evaluation method for discomfort glare caused by the dark area illuminated by sunlight in the sunshade canopy, and the results showed that the glare value UGR of the equal-distance sunshade canopy was smaller than that of the unequal-distance sunshade canopy. [PERSON] [13] studied the anti-glare plant height calculation method in the central partition of the access zone, to replace engineering anti-glare facilities and achieve better ecological and landscape benefits. [PERSON] et al. [14] analyzed the glare effect caused by the unreasonable luminance transition at the exit zone, and proposed a gradient layer design method based on the anti-glare principle. It can be seen from the above that the current research on the external luminance L\({}_{20}\)(S) of the east-west highway tunnel has been limited to expounding the variation of the external luminance value of the east-west road tunnel. Due to the particularity of tunnel orientation, it has a certain impact on traffic safety, but the relationship between east-west orientation factors and the variation rule of L\({}_{20}\)(S) outside the tunnel has not been studied in depth. At the same time, the studies on the glare phenomenon of the highway tunnel have been basically limited to the \"black-hole effect\" in the tunnel entrance section, the glare of lamps inside the tunnel, the \"white-hole effect\" in the tunnel exit section, and the anti-glare measures of the engineering outside the tunnel. At present, there are few corresponding studies available on the relationship between the glare of different orientations and the time-varying characteristics of the luminance L\({}_{20}\)(S) outside the tunnel. Therefore, the influence of indirect glare caused by luminance difference inside and outside the tunnel and the surroundings outside the tunnel on the visual environment quality of the access zone has been ignored. Currently, a lot of the research on tunnel glare is based on the analysis of a 20\({}^{\circ}\) line of sight angle. That is, when the angle between the glare source light and the driver's line of sight is 20\({}^{\circ}\), theoretically, it is easy to produce glare phenomenon. But this theory only applies to fixed direct glare light sources, such as lighting fixtures and other devices. However, the glare produced by the landscape and road surface outside the tunnel is irregular, and it is difficult to determine the angle of glare by the above theory. Combined with the east-west orientation factor, sunlight will be directly on the tunnel portal in the morning and afternoon, making the 20\({}^{\circ}\) field of view brighter outside the tunnel surroundings and road surface forming an indirect glare. Combined with the large luminance difference between inside and outside the tunnel, the driver's visual load will be increased in this case, and it will directly affect the driving safety and comfort of the access zone. In terms of luminance outside the tunnel, CIE 88-2004 [15] proposed a field of view range of 20\({}^{\circ}\) of human vision based on the stopping sight distance from the tunnel entrance, in which the 20\({}^{\circ}\) field of view covers the 20\({}^{\circ}\) angle between the glare light source and the driver's line of sight that is prone to glare. That is, the glare phenomenon readily occurs in the 20\({}^{\circ}\) field of view of the external brightness proposed by CIE. The 20\({}^{\circ}\) field of view of the external luminance L\({}_{20}\)(S) can solve the problem where it is difficult to determine the angle of glare. At the same time, the division principle of the landscape inside and outside the tunnel in the 20\({}^{\circ}\) field of view just divides the indirect glare light source and the glare background outside the cave. Therefore, the 20\({}^{\circ}\) field of view proposed by CIE is used in this study to analyze the time-varying characteristics (trend and rule) of the external luminance L\({}_{20}\)(S) and uncomfortable glare in the access zone of the east-west road tunnel.