21. On a roadway with two or more lanes of traffic in the same direction, the driver of a low-speed vehicle must travel in the same direction as traffic and in the far right lane, except:
(1) if he is making a left turn;
(2) if the lane on the extreme right is reserved for other types of vehicles, is obstructed or closed to traffic, in which case he must drive in the lane next to the extreme right lane.
For the purposes of the first paragraph and in every case in which he is required to change lanes, the driver must, using his turn-signal lights, signal his intention over a sufficient distance so as not to endanger his safety and the safety of other users of a public road, and ensure that he can perform the manoeuver without risk.