The Characteristic Of Fog Extinction In Expressway And Impact On Traffic Safety

The traffic safety in fog area along expressway is a worldwide issue. The cost of crash involvement by fog is quitely large in our country. With the development of expressway and the growth of automobile, the crash involvement rate has also increased. Enhance the traffic safety caused by reduced visibility is a big task, and it has a significant economic and social benefits.According to the definition of ambient fog and its forming characteristics, conditions and features of the fog forming in the areas along some expressways are pointed out. With the Lambert-Beer law and the relative luminance contrast equation, course of visibility reduction and traffic safety influenced by fog is analyzed. The relations among extinction,visibility and traffic safety are further analyzed. The physical factors of the extinction are established, such as number density of the fog droplet, moisture in fog, mass concentration, fog diameter; The environmental factors are mainly air temperature, incident light wavelengh, altitude and so on. The flux of motor vehicles and wind speed are the indirect factors of the extinction. The measured data of fog are analyzed with the statistical method. The quantitative relation among extinction, number density of the fog droplet, moisture in fog, mass concentration, fog diameter, air temperature are obtained. Moreover, Analytical Hierarchy Process is used to calculate the power of the extinction impact factors, the result is: number density(52.83%), moisture in fog(34.9%), the average diameter(4.11%), air temperature(8.15%).The flaws of our traffic manage and the suggestions for them are pointed out baced on our practice traffic manage of expressway and the advanced fog managements in the U.S.A..