Influence of solar glare intensity on vehicular speed variance

Studies in weather-affected traffic collisions have mainly focused on rain and snow, which can be referred to as highly variable and non-recurrent events. On the other hand, although solar light is among the natural phenomena that regularly and negatively influences the physical and mental health of drivers, research efforts to quantitatively examine the effect of solar glare on traffic collisions are insufficient. Therefore, this study investigates that sunlight interferes with the driver’s vision, causing speed variance, which increases the likelihood of a traffic accident.
A comprehensive methodology was proposed to determine the temporal range where solar glare affects driving with respect to the position of the Sun, road geometry, and driver’s field of vision with the aid of GIS analysis. Besides, vehicle speed variance, which is a traffic flow characteristics and a risk factor involved in traffic collisions, during traffic conditions affected and unaffected by solar glare were statistically evaluated using ANOVA tests. Then, the proposed methodology was verified and confirmed taking 20 segments of the Namhae Expressway in Busan, Korea, as a case study.
Results of the study showed that vehicle speed variance was statistically greater when it was affected by solar glare than when not affected, and this effect was more pronounced on westbound segments than in eastbound segments. This is because solar glare influences eastbound traffic early in the morning, when traffic demand is not high enough to interfere with driving. On the other hand, westbound traffic is affected during the evening commute, when much more vehicles influence driving conditions.
The study concludes that vehicle speed variance due to solar glare takes place, and can be temporally and spatially identified on all east-west roads. It was found that the speed deviation was greater during the time affected by the sun glare, which can increase the probability of traffic accidents like investigated in the related study efforts. Particularly, because westbound traffic is more heavily affected by solar glare than eastbound traffic, more active measures should be implemented and proactively reflected in designing road geometry to improve traffic safety.