When it is not possible to see distinctly up to a distance of 200m, the formation of armed forces on march and of all other groups of pedestrians such as procession or school children groups in lines under the supervision of a school master, when they move on the roadway with more than one front, must be signaled by the white light held on the left side in front and red light held on the left side at the back but the sides of these units or groups must, where their length is superior to 6m, be signaled by: