While backing up, a driver should constantly check their what?

When backing up, a driver should constantly check their mirrors. This is crucial for maintaining awareness of their surroundings, as mirrors provide a view of areas that may not be visible directly out of the rear window. Checking mirrors helps identify pedestrians, obstacles, or vehicles that may be approaching from behind or from the sides, which can prevent accidents or collisions while maneuvering in reverse.

By using mirrors effectively, drivers can gauge the distance to objects and ensure they have sufficient space to back up safely. This practice aligns with safe driving principles, emphasizing awareness and caution, especially in potentially hazardous situations like reversing. Other options, such as the steering wheel, mile markers, or the dashboard, do not provide the necessary situational awareness that mirrors do when it comes to backing up safely.