What is the meaning of the following traffic sign?

1. Road works - drive in the direction of the appropriate arrow.
2. Lane is closed. No driving in the lane under the traffic sign.
3. Correct answer: Merge with the traffic in the adjacent lane, from either right or left.
4. A hairpin turn, either left or right.

WhyTwo diagonal arrows tell you to merge into the adjacent lane on the left or right. The lane itself is not necessarily closed.