## 5 Conclusions  
This study focuses on the glare phenomenon in the access zone of east-west oriented road tunnels and the time-varying characteristics of the L\({}_{20}\)(S) value of the luminance outside the tunnel. Through field tests, we analyzed the difference in luminance within and outside the tunnel. We focused on a 20\({}^{\circ}\) field of view from the human eye at a stopping sight distance from the tunnel entrance. The difference and time-varying characteristics between the measured and recommended values of luminance outside the tunnel were analyzed. The conclusions obtained are as follows:  
1. The time-varying characteristics of L\({}_{20}\)(S) in the access zone generally increase first and then decrease, and the maximum value of L\({}_{20}\)(S) in the east-oriented and west-oriented tunnels occurs at 11:00 a.m. and 14:00-16:00 p.m., respectively.
2. The difference in the luminance of the contribution ratio outside and inside the tunnel is more than 95.7% in the morning (9:00 a.m.-11:00 a.m.), and the maximum is nearly 97%, while the difference in the luminance of the contribution ratio is smaller in the afternoon than in the morning. The contribution ratio of the luminance outside the road tunnel due west reaches the maximum at around 16:00 p.m. In addition, the luminance difference between the interior and exterior of the east-west oriented road tunnel generally increases first and then decreases.
3. When the surroundings in the access zone of the east-west oriented road tunnel are subjected to direct sunlight, the visual environment presents an inappropriate luminance phenomenon due to the increased luminance difference between the inside and outside of the tunnel, resulting in uncomfortable glare and intolerable glare within the 20\({}^{\circ}\) field of view. And the situation will get worse after rainfall. If the glare problem is not controlled, it will affect driving safety and comfort.
4. The test methods can serve as a reference for studying and designing visual environment quality, glare control, luminance L\({}_{20}\)(S) outside the tunnel and the surroundings of the tunnel. Simultaneously, the application of a 20\({}^{\circ}\) field of view and quantified indirect glare source research techniques pave the way for investigating the non-luminaire outside the tunnel glare and glare from other external structures.
5. In the lighting design of the east-west oriented road tunnel, the impact of uncomfortable glare near the tunnel on the visual environment should be considered. It is advisable to select pavement materials with low reflectivity and arrange dark vegetation. This approach can reduce the brightness difference between the tunnel interior and exterior, enhancing driver safety and comfort.  
Due to limitations in the experimental conditions, this experiment was unable to obtain very rich data. In the future, testing will be conducted under different weather conditions in spring, summer, autumn, and winter. In addition, the author plans to conduct research in areas with different altitudes and latitude in the future, exploring the impact of altitude and latitude on the brightness and glare issues outside the access zone of east-west oriented tunnels. For future work, the author is also considering establishing a model to evaluate the level of glare outside the tunnel.  
[PERSON] wrote the manuscript, [PERSON] designed the proposed control strategy and conceived the structure of the paper, [PERSON] and [PERSON] gave suggestions for this paper. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Nature Science Foundation of China under Grant No. 52378391.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.