A method of collaborative simulation of the train collision process using a rigid motion model and a flexible collision model is proposed to solve the problem of the low computational efficiency of the finite element numerical simulation of the train collision process. This study investigated the collision response of a train derailment hitting a platform with different curve radii based on an accident in which a subway train derailed and hit a platform. Based on the results, a collision damage index is proposed to assess the relative degree of damage of train derailment collisions at different curve radii. The results reveal that within a certain radius of the curve (when the impact distance D exists), there is a positive correlation between the curve radius and the collision damage index, and when the curve radius exceeds a certain value (when the impact distance D doesn’t exist), the train and platform don’t collide.