In what scenario is it MOST important to check your mirrors frequently when driving a commercial vehicle?

Checking mirrors frequently is most critical when changing lanes or merging because these maneuvers significantly increase the risk of collision with surrounding vehicles. Commercial vehicles, which are larger and have larger blind spots compared to passenger vehicles, require the driver to be highly aware of their surroundings to ensure safe movement.

When changing lanes or merging, the driver needs to assess the position and speed of other vehicles, identify potential obstacles, and ensure there is enough space to execute the maneuver safely. This frequent checking helps the driver to stay aware of vehicles in adjacent lanes as well as those approaching from behind, allowing for informed decisions that help avoid accidents.

While checking mirrors is always important—during long trips, while parked, and on open roads—those scenarios do not present the same immediate need for situational awareness and quick reaction that changing lanes or merging does. Therefore, in the context of maintaining safety and preventing collisions, mirror checks are paramount during these specific driving actions.