Experimental study on obstacle visibility and driving safety in lighting environment of road tunnel interior zone

Traditional tunnel lighting luminance is obtained from the static observation experiments for an obstacle without consideration of the visual characteristics of human eyes in dynamic state. The visual performances of human eyes during vehicle moving are quite different from those in static condition. Therefore, the influence of vehicle speed on the visible distance of human eyes for an obstacle in tunnel interior zone was experimentally analyzed in this study. Then, the visible distance was compared with the stopping distance specified in the current lighting specifications and the driving safety in tunnel was discussed. The results show that the visible distance for an obstacle under the illumination of LED lamps or vehicle headlights during driving is significantly smaller than that in static condition. In the LED lighting environment, the visible distance for an obstacle on road pavement at the vehicle speeds of 40 km/h, 60 km/h, 80 km/h and 100 km/h compared with that at the speed of 0 decreased by more than 8 %, 16 %, 23 % and 31 %, respectively. The lighting brightness setting in a tunnel should fully consider the impact of driving speed on human visual performance. For the road tunnel with a speed limit of less than 60 km/h, even if only the vehicle headlights are used, the observers can recognize the obstacle at a distance greater than the stopping distance. In view of the huge burden of energy consumption for tunnel lighting at present, it is suggested to apply the combination lighting of LED lamps and vehicle headlights to reduce the lighting energy consumption. For the road tunnel with a design speed limit of more than 80 km/h, the setting of lighting brightness on road surface according to the luminance values specified in the existing lighting specifications cannot guarantee driving safety. Future research should solve the problem that the visible distance of human eyes for an obstacle is less than the demand of stopping distance when driving in tunnel interior zone without increasing the lighting energy consumption.