When is it legal to pass on the left?

Passing on the left is legal under several conditions, which include all the mentioned scenarios. When traffic is clear, it ensures that there is enough space and visibility to perform the maneuver safely. This reduces the risk of a collision as you are not overtaking another vehicle in congested traffic.

Additionally, when the other driver signals, it can indicate their intention to turn or change lanes, which provides you with essential context about their movement. This signaling can often make passing safer, as it informs you of the other vehicle's actions.

Furthermore, when there are no traffic signs prohibiting passing, it means you are in a designated area where overtaking another vehicle is permitted. Signs are placed for safety, indicating where passing could be dangerous due to road conditions or traffic patterns.

Thus, all these factors play a critical role in ensuring that passing on the left is done legally and safely, which is why the answer encompasses all of them.