A two-lane highway has a high rate of head-on collisions, sideswipe collisions, crashes with an fixed object. This study was to analyze the weakness of a cross section and a horizontal curve in a two-lane highway and find countermeasures to improve the traffic operations and safety. This study evaluated the effectiveness of widening, curve flattening and superelevation, verified it with a case study and assessed the economical efficiency. This study selected the difference between tangent section operating speeds and curve section operating speeds as an evaluation index of horizontal curve section in a two-lane highway. The results indicated that curve flattening is the best way to improve the traffic safety in a two-lane highway. This study has implication that it provides the quantitative effects of curve flattening. Also directions for future study were discussed.