On a single laned road (as shown), you must always overtake another vehicle on its right except when:

• A. The other vehicle is turning right.
  Explanation:

  "You can overtake a vehicle on its left when it is waiting to turn right. You can also overtake on the left if you are travelling in marked lanes and the lane on the right is travelling slower than the lane on the left."
• B. You are travelling at more than 80 km/h.
• C. The other vehicle is going slower than you.