They are those whose purpose is to regulate the use of one-way lanes; when due to variations in the flow of dual-traffic traffic; certain lanes can be used for movement in one direction for a few hours and for the opposite direction during other hours. these devices are distinguished by having traffic lights on each of the lanes and by their different shape and symbol (arrow pointing downwards and an x-shaped cross) and complementary signs are generally used to explain their purpose and operation. the direction of movement of one lane vehicles; it should only be reversed or made reversible after a road engineering study;