PURPOSES : The purpose of this study was to analyze the visibility of lanes according to the changes in the plane and longitudinal line of roads considering the horizontal and vertical diffusion angles of vehicle headlights at night. First, the visibility length of the lane was determined according to the plane linearity of the road such that it could be applied to simulation and visualization data. Second, the night vision length of the lane was established according to the longitudinal line of the road such that it could be applied to the simulation and visualization data. METHODS : In this study, each variable is first examined to consider the horizontal and vertical diffusion angles of the vehicle headlights. Second, the equation for the visibility of the lane by vehicle headlights in planar linearity is obtained, and the visibility of the lane is determined. Third, an equation is obtained for the visibility of the lane by vehicle headlights in longitudinal linearity. RESULTS : The results of this study are as follows. First, the visibility length of the lane in the section where the plane linearity of the highway existed at night was studied. In this case, the visibility length of the right and left lanes based on the vehicle decreased according to the plane linearity of the highway. Second, the visibility length of the lane in the section where the longitudinal line of the highway existed at night was investigated. In this case, the visibility length of the lane decreased according to the change in the longitudinal line of the highway. CONCLUSIONS : Considering the horizontal and vertical diffusion angles, the visibility length of the lane was determined according to the changes in the plane and vertical line of the road. It can be applied to simulation and visualization data. In general, the visibility length considering the spread angle of the vehicle headlights was shorter than the visibility length of the lane by the headlights; roads must be designed in consideration with the above result.