## 2 Literature Review
In this way, several studies have verified that conditions such as the intensity of road lighting or color temperature can change the driver's visibility, but there is a limitation in that the experiment was conducted only under normal conditions. Even though road lighting is the only solution in adverse weather conditions at night, in fact, little research has been conducted on road lighting visibility in lighting environments such as rain and fog [18]. Most studies are conducted on the relationship between adverse weather and traffic accidents based on past records. The reason may be economic considerations, and it is presumed that there is a lack of related research because there are few facilities that can implement real-scale rain and fog. In fact, the fact that there is currently no official method to evaluate road lighting during adverse weather may be seen as a further reason for research and development on road lighting during adverse weather. CIE proposes a method for measuring and calculating the luminance of road surfaces using a luminance meter in CIE 114-2000 [1] and sets standards for classifying road lighting grades based on the luminance of road surfaces measured in CIE 115-2010 [2]. However, this standard is based on normal conditions and is not suitable for adverse weather. The method presented by CIE suggests that the higher the road surface luminance, the higher the class of high-quality road lighting, but this measurement method is not suitable when applied in adverse weather. To analyze the effect of weather on road luminance, there is a previous study that measured road surface luminance under various weather conditions [19]. As a result, it was confirmed that road surface luminance increased significantly on wet, snowy, and foggy roads compared to dry roads. Even though the luminance of the road surface increased compared to the dry road surface, it is difficult to say that the situation is one in which the driver has better visibility than the dry road surface situation. In other words, the existing evaluation method may be judged to be unsuitable in adverse weather. The reason why it is difficult to evaluate road lighting performance in the same way as under normal conditions during adverse weather is because the level of road surface luminance varies depending on the measurement point due to diffuse reflection of the road surface in adverse weather conditions, and it is impossible to extract accurate road surface luminance values due to light scattering in the atmosphere. CIE 115-2010 states 'The purpose of road lighting is to provide revealing obstacles' and 'there is a need to reveal extraneous objects that suddenly appear on the road'; it is expressed that good quality road lighting provides an appropriate distance to recognize obstacles [2]. In fact, there are research cases that have identified through subject experiments that obstacle recognition distance increases as lighting performance improves [20], and there are studies that have identified through empirical experiments that obstacle recognition distance can change by applying various road lighting during adverse weather [9]. Additionally, there are empirical research results showing that the higher the color temperature of road lighting during fog, the higher the obstacle visibility [21]. Therefore, this study proposed obstacle recognition distance as a measure of effectiveness of road lighting performance evaluation in adverse weather that can replace the existing road surface luminance measurement method, and empirical experiments were conducted to determine whether obstacle recognition distance shows effective differences according to changes in road lighting conditions during adverse weather.