Abstract: Because of the influence of the basic railway boundaries and security requirements of dynamic turning, the configuration and complex centroid of special vehicles in rail transportation must satisfy the railway boundaries. Focusing on these problems, the boundary design of special vehicles was studied in this article.A mathematical model was derived to calculate the design shape and dimension range of the three-dimensional configuration, including profile- or centroid-centered loading.The largest three-dimensional envelopment configuration for multiple loading modes was designed. Moreover,through the study of the centroid height envelopment area, it was concluded that the centroid height of vehicles between 60 t and 70 t should not exceed 1284~1213 mm, thereby providing a basis for the optimal configuration and centroid for vehicle design.

Key words: railway boundaries, boundary restriction, static and dynamic check, envelopment area, three-dimensional envelopment configuration