What is the primary purpose of using a seatbelt?

The primary purpose of using a seatbelt is to ensure safety during a collision. Seatbelts are designed to secure occupants in their seats, preventing them from being ejected from the vehicle or colliding with other parts of the car during an accident. In the event of a crash, a seatbelt significantly reduces the risk of serious injury or death by restraining the body's movement and helping to distribute the forces experienced in a collision over more durable parts of the body.

In contrast, while speeding, fuel efficiency, and vehicle weight are considerations for vehicle operation and design, they are not the primary functions of a seatbelt. The focus of seatbelt use is safety, highlighting the importance of occupant protection in preventing injuries in crashes.