I. Introduction
How to avoid vehicle collision accidents and ensure driving safety is one of the most important research topics in the field of automobile safety assistance driving system and even unmanned driving system. The root cause of the collision accident is that two or more traffic elements have reached the same spatial coordinates at the same time, and the basic attributes and motion attributes of the units that collide at the same time determine the severity of the collision accident [1]. In order to avoiding collision accidents, two goals should be achieved: (i) the time of each traffic unit when it reaches the same spatial coordinates is different from each other, or (ii) each traffic unit should be in different spatial coordinates at the same time. The first goal can be achieved by traffic control, e.g., traffic rules at intersections, lane use settings [2]. For the second goal, how to control the distance among various traffic units within a reasonable range by a reasonable way becomes critical [3].