Design Method of Combined Gradient Dimming Structures for Highway Tunnels

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Design Method of Combined Gradient Dimming Structures for Highway Tunnels

Liang, Bo / Xiao, Jinghang / Niu, Jia’an / Li, Shuo / He, Shiyong

The notable brightness difference between the inside and outside of a tunnel is a major issue restricting the safe driving and energy-saving conditions of highway tunnels. The installation of a shading structure at the entrance of a highway tunnel could resolve this problem. This method is equivalent to moving the entrance zone outside so that light is smoothly transmitted into the tunnel, which is called pretunnel lighting. In this research, the shading structure is selected as the research object. First, the shading effects of pergolas and sunshades of different cross-sectional forms are analyzed. Second, choosing the Jiulongpo Tunnel in Chongqing as an example, through DIALux software modeling and analysis, the tunnel sunshade is selected as the primary shading structure, which is better than the pergola in terms of the average luminance value and uniformity of luminance. Third, based on the idea of gradient dimming outside the tunnel, three kinds of combined gradient dimming sunshades are designed. Considering the influence of the season, weather and orientation, the optimal design scheme is determined in detail. Finally, the energy-saving benefits are calculated of the installation of a tunnel sunshade to replace the enhanced lighting in Threshold zone 1 (TH1) combined with gradient dimming lighting in Threshold zone 2 (TH2). The results show that the combined gradient dimming sunshade in Scheme 3 (70% + 40% + 20% + 10%) is optimal. The combined gradient dimming sunshade could decrease the variation in luminance inside and outside the tunnel and reduce the artificial lighting intensity in the entrance zone, which could facilitate safe driving and energy savings.