What should you check for proper mirror adjustments?

The importance of checking for visibility of 200 feet or 4 bus lengths when adjusting mirrors lies in ensuring that the driver has adequate awareness of the surrounding environment. Proper mirror adjustments are critical for safe driving, especially for a large vehicle like a school bus. Being able to see clearly to the rear and sides helps in detecting pedestrians, including children, as well as other vehicles and obstacles that may not be immediately in the bus's direct line of sight.

When you ensure that your mirrors allow for this level of visibility, you are significantly reducing the risk of accidents. This guideline helps establish a framework for proper mirror setup, as it allows for maximum awareness of your vehicle's immediate surroundings while on the road.

The other options may relate to aspects of mirror use, but they do not directly address the fundamental requirement of having a clear safety margin visible through the mirrors. For example, being able to see the front of the bus could be less practical for understanding the immediate environment behind and to the sides. Visibility of flashes from headlights doesn't contribute to a driver's situational awareness in the context of mirror adjustments, and proper alignment with road markings, though important, does not encompass the critical factor of awareness over distances needed for safe maneuvering.