Review on Visibility Monitoring in Expressway under Foggy Condition

Visibility monitoring under foggy condition is very essential to traffic safety on expressway. The definition and influence factor of visibility are summarized. The main advantages and disadvantages of three common methods- transmission method, scattering method, digital imaging method and related visibility meters are analyzed and compared here. The domestic and foreign status and trends of visibility research on foggy expressway are mainly introduced from thick fog forecast, warning and monitoring system, visibility detection device. Aiming at the existing problems of visibility monitoring in expressway, some suggestions for improvement are put forward at last.