In what circumstance must a vehicle operator use a spotter according to operational guidelines?

The requirement for a vehicle operator to use a spotter is particularly critical when near potential hazards in a confined space. This is primarily due to the increased risks associated with limited visibility and the potential presence of obstacles or persons that may not be immediately visible to the vehicle operator. In confined spaces, operating a vehicle can lead to accidents if the driver is unable to see a spot that the spotter can, such as nearby walls, other vehicles, or individuals. The spotter serves as an additional set of eyes, helping to monitor the surroundings and ensure safe maneuvers.

In contrast, the other choices either do not emphasize the necessity of having a spotter or describe scenarios where operating a vehicle might not require the same level of precaution. For example, traveling on highways typically involves more open space with little to no obstacles compared to confined spaces, and driving alone or when visibility is clear doesn't inherently necessitate an additional person to assist. Thus, the context of confined spaces with potential hazards makes the need for a spotter essential for safety.