Abstract: This study analyses the current horizontal curve design parameter based on psychology and physiologic theories, the experimental data is measured by using advanced physiological signal measurement apparatus as they drive on a two-lane highway in a mountain area, and then the reasonable thresholds of horizontal curves radius are obtained and verified using experimental data in this study. The thresholds realize the human design and decrease traffic accidents, which reflect the psycho-physiological characters of the drivers on two-lane highway in the mountain area.