What is the purpose of box junctions and when may you enter one?

Answer: C — To prevent the junction becoming blocked, you may only enter if your exit is clear; also, you may wait in a yellow box junction when oncoming traffic prevents you turning right

Box junctions are designed to keep busy intersections clear in order to prevent gridlock and allow traffic to flow smoothly. This is why option C is the correct answer. Options A and D are incorrect because they do not accurately describe the purpose of a box junction. Option B is also incorrect because it suggests that drivers can enter a box junction at any time, which could lead to congestion and accidents. It's important to only enter a box junction if your exit is clear and, in some cases, you may be allowed to wait in a yellow box junction if you are unable to turn right due to oncoming traffic. Remember to always follow the rules of the road and adhere to the purpose of box junctions to keep traffic moving efficiently.