Safety Evaluation of Illuminance Transition at Highway Tunnel Portals on Basis of Visual Load

Highway tunnel entrances and exits are accident-prone locations, especially in the daytime, primarily because of the sharp transitions in lighting in these areas. Therefore, a rational assessment of lighting transitions at tunnel portals is the key to ensuring traffic safety. This study used the EMR-8B eye-tracker system to monitor the pupil changes of eight selected drivers as they drove through 26 typical highway tunnels. The test results showed a power function relationship between drivers’ pupil areas and pupil illuminance at highway tunnel portals. A quantitative relationship between the pupil area and its critical velocity was also established, and the ratio ( k) of the pupil area's changing rate in relation to its critical velocity was used to assess the visual load and to further evaluate the lighting transitions. The results demonstrated that ( a) the relationship between pupil illuminance at the tunnel portal and the driver's pupil area conformed to Stevens’ law from experimental psychology, ( b) the relationship between the driver's pupil area and its critical velocity followed the quadratic function, ( c) the visual load at a tunnel entrance was heavier than that at the tunnel exit, and ( d) the severe transitions in pupil illuminance within 10 m of some existing highway tunnel entrances caused a great visual load, and thus are urgently in need of improvement.