Whenever special pedestrian-control signals exhibiting the words “Walk” or “Don’t Walk” or the illuminated symbols of a walking person or an upraised palm are in place such signals shall indicate as follows:
     (a) Walk or walking person symbol. Pedestrians facing such signal may proceed across the roadway in the direction of the signal, and shall be given the right of way by the drivers of all vehicles.
     (b) Don’t Walk or upraised palm symbol. No pedestrian shall start to cross the roadway in the direction of such signal, but any pedestrian who has partly completed his crossing on the Walk signal or walking person symbol shall proceed to a sidewalk or safety island while the “Don’t Walk” signal or upraised palm symbol is illuminated, steady, or flashing.