Fig. 6

Illustration of the CBDR principle. Two vehicles A and B are driving on straight paths that intersect at the point I, each with their own constant speed. If the bearing α of vehicle B viewed from vehicle A remains constant at all times, the vehicles are going to reach the intersection I simultaneously, i.e. they are going to collide. Note that, by symmetry, this also means that the bearing β of vehicle A is constant. If the bearing α decreases with time, vehicle B will have passed the intersection when vehicle reaches it (this is only true in a strict sense if we neglect the size of the vehicles). Conversely, if α increases, vehicle B will not yet have reached the intersection. Note that these rules are valid irrespective of the angle γ between the straight paths