What is the purpose of a seat belt?

The primary purpose of a seat belt is to restrain occupants and reduce the risk of injury during a vehicle collision or sudden stop. Seat belts are designed to secure the occupant in their seat, preventing them from being thrown forward or ejected from the vehicle in the event of an accident. This critical safety feature significantly decreases the likelihood of severe injuries to the head, neck, and torso by spreading the forces of a crash across stronger parts of the body and helping maintain proper body position.

The other choices do not effectively capture the main function of a seat belt. While keeping the driver alert may be a benefit of good traffic safety practices, it is not the role of a seat belt. Comfort for passengers could be a byproduct of wearing a seat belt, but it is not its purpose. As for ensuring the car doesn't exceed speed limits, this is unrelated to seat belt functionality, which specifically pertains to occupant safety rather than vehicle operation or speed regulation.