Methodology to Analyze Sun Glare Related Safety Problems at Highway Tunnel Exits

Good visibility of the road and its surroundings is a basic requirement for safe driving. Glare caused by direct sunlight interferes with drivers' vision performance. In high-glare conditions the visibility of objects is reduced thus increasing the probability of occurrence of incidents and crashes. Critical sections of existing or newly designed roads need to be analyzed in order to prevent these problems. The research presented in this paper provides a practical method to evaluate potential driver vision impairment situations caused by sun glare at tunnel exits. The methodology is based on the projection of the solar paths on a cylindrical chart; other geometrical variables involves in the model are also represented on the same projection. An application to an existing Spanish motorway tunnel is presented. Results show that the methodology can be successfully employed (1) to identify possible sun glare related problems; (2) to analyze different mitigation alternatives; and (3) to design physical countermeasures to avoid driver exposure to sun glare inside the tunnel and at its exit.