Passing on both sides of a highway is not allowed when:

Answer: A — There are dashed white lines on both sides

Passing on both sides of a highway is not allowed when there are dashed white lines on both sides because dashed white lines indicate that passing is prohibited in both directions. These lines represent the centerline of the road and are meant to separate traffic moving in opposite directions. When there are dashed white lines on both sides, it is unsafe and illegal to pass on either side as it increases the risk of head-on collisions. Solid yellow line markings on both sides (choice B) usually indicate a no-passing zone in both directions. A one-way street (choice C) typically allows passing on one side of the road, as traffic is only moving in one direction. Having no shoulder on either side (choice D) does not necessarily determine whether passing on both sides is allowed or not.