What it is: Seatbelts, including shoulder harnesses, are the first line of defense against injury in an automobile accident. Manufactured from strong synthetic webbing, they help hold the wearer in place during a collision, helping to control their rate of deceleration. All outboard seating positions on new vehicles feature seatbelts that are integral with shoulder harnesses (although some center belts on bench seats do not).
How it works: A surprising number of technologies have improved seatbelt design since their inception many years ago. Emergency Locking Retractors (ELR) allow the wearer freedom of movement while driving, but lock the seatbelt in place in a collision. Automatic Locking Retractors (ALR) allow manual locking of the seatbelt to secure a child seat. Pretensioners use a pyrotechnic device to pull the seatbelt tight immediately following a collision. And force limiters allow the seatbelt to "stretch" during a collision to more gradually decelerate the wearer.
How it benefits the passengers: The seatbelt's first and most important task is to keep the wearer in place during a collision, helping reduce the chance that he or she will be ejected from the vehicle or strike other occupants or injurious surfaces inside the car. Technologies like pretensioners and force limiters enhance their ability to control the wearer's rate of deceleration in an accident.