With its advantages of taking up less land, producing less pollution and providing better protection for important urban landscape, underground expressway has become a new solution for traffic problems in many cities in China. In the crossed channel program proposed to solve traffic problems in downtown area of Shanghai, a 7.8-km East-West channel with a 6.1km portion under the ground is a critical component, in which illumination significantly affects the legibility of traffic signs. For traffic signs at entrance to underground expressway, luminance characteristics of different reflective film combinations were compared and anti-glare performance was studied. The relationship between luminance and sign legibility was obtained. As to traffic signs in underground expressway, this research compared several signs to obtain the most appropriate traffic sign scheme. It was concluded that semi-permeable internal illuminated sign scheme is the optimal choice for underground expressway. An appropriate luminance range for recommended sign scheme was also determined.
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