Calculation method of overtaking sight distance for dual-lane highway

5 factors affecting the overtaking sight distance of dual-lane highway were analyzed from the view of safe driving. The running sketch map of overtaking car, overtook car and opposite car on dual-lane highway was designed. The mathematic model of calculating overtaking sight distance for overtaking car from beginning overtaking to finishing overtaking was established. The calculating parameters were defined such as braking distance and space headway on same lane etc, and the specific calculating formula of overtaking sight distance was proposed by means of mathematic analysis method. According to different design speeds and driving speeds, the overtaking sight distances of car and truck on dual-lane highway were calculated. Analysis result indicates that the overtaking sight distance of dual-lane highway is concerned with the design speed of highway, the overtaking speed of overtaking car, the speeds of overtook car and opposite car, and space headway on same lane. When the speeds of overtook car and opposite car are less than a half of overtaking speed, the calculated value of overtaking sight distance is just close to its specified value. Specified overtaking sight distance of dual-lane highway is smaller from safety view.