The operator of a vehicle shall, before stopping, turning, or changing the course of such vehicle, see that there is sufficient space to make such movement in safety. If any pedestrian might be affected by such movement, the operator shall give a clearly audible signal by sounding the horn, and whenever the operation of any other vehicle may be affected by such movement, he shall give some unmistakable signal to the driver of all other vehicles of his intention to make such movement. (Ref. 60-6,163 RS Neb.)