What is the restriction on dual passing on the roads?

The correct understanding of the restriction on dual passing on the roads is that it is prohibited when a vehicle is passing another. This rule is in place to ensure safety on the roads by preventing potential collisions and confusion that can arise when multiple vehicles attempt to pass simultaneously, especially in situations where visibility is limited or the road conditions are not ideal.

In terms of road safety, allowing dual passing while one vehicle is already in the process of passing could lead to dangerous situations, as vehicles may not have the necessary space or time to maneuver safely. Therefore, this regulation is aimed at maintaining orderly traffic flow and minimizing accidents.

The other choices reflect misconceptions about dual passing rules. Allowing dual passing when safe or only in designated zones does not align with the core intent of the regulation, which emphasizes the prohibition to maintain clear and safe conditions on the road. Always allowing dual passing disregards the important safety considerations that the prohibition serves.