3.2.3. Situation for the descending of limited speed
In particular, a special case that the train is on a segment with descending limited speed should be considered. As is illustrated in Fig. 4, the limited speed will descend for the gradient, curve, tunnel, etc. Thus, we should make the following decisions in advance to prevent that the speed of train exceeds the limited speed. According to the knowledge from drivers, when the limited speed descends, there must be a judgment of deceleration in advance. We define a safe distance, which can be estimated based on the state of the train: