What is the primary purpose of the rearview mirrors on a tractor-trailer?

The primary purpose of the rearview mirrors on a tractor-trailer is to allow the driver to see traffic behind and alongside the vehicle. This is crucial for safe driving, as large vehicles have significant blind spots. By providing a clear view of the area to the rear and sides of the truck, these mirrors enable drivers to make informed decisions when changing lanes, merging, or backing up. Proper mirror use is essential for maintaining awareness of surrounding traffic and ensuring that the driver can navigate safely in various driving conditions.

Other options focus on functions that are not primarily related to the role of mirrors. Adjusting the driver's seat position does not involve the mirrors, and while reducing wind resistance is important for efficiency, mirrors are designed for visibility, not aerodynamics. Serving as a warning signal to other drivers is also not the primary function of mirrors; they are intended mainly for enhancing the driver's awareness rather than acting as indicators for others.