Abstract: In order to evaluate the objective safety of road alignment synthetically,according to the influence of the space geometric characteristic index of the horizontal,vertical and cross-sectional alignment index on speed and safety and considering the driving behavior,the horizontal,vertical and cross-sectional alignment comprehensive index functions are set.Based on the space geometric theory and the alignment design characteristics,the three-dimensional road alignment comprehensive index description models including curvature,curvature variation,the angle of curve,grade and lane width are established by using the mode of horizontal,vertical index as primary and the cross-sectional index as correction.At the same time,the influence of the bridge and the tunnel are also considered.Three-dimensional space description modeling of alignment comprehensive index solves the key technical problem of operating speed prediction and alignment safety evaluation.