SEAT BELTS

1. A seat belt or seatbelt, sometimes called a safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop.
2. As part of an overall automobile passive safety system, seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle, or other passengers (the so-called second impact), are in the correct position for the airbag to deploy and prevent the passenger from being thrown from the vehicle.
3. Seat belts also absorb energy by being designed to stretch during any sudden deceleration, so that there is less speed differential between the passenger's body and their vehicle interior, and also to spread the loading of impact on the passengers body.
4. The final, so-called 'third impact' after a passenger's body hits the car interior, airbag or seat belts, is that of the internal organs hitting the ribcage or skull. The force of this impact is the mechanism through which car crashes cause disabling or life threatening injury.
5. The sequence of energy dissipating and speed reducing technologies - crumple zone - seat belt - airbags - padded interior.They are designed to work together as a system to reduce the force of this final impact.

HISTORY ABOUT RESTRAINT SYSTEM

1. Automobiles entered the market more than 100 years ago. Since then, tremendous progress in reliability,usability, and safety of roadway vehicles has been made. 
2. Over the last 20 years, the automotive safety industry has gone through considerable changes.In recent years, passive restraint systems have been one of the fastest-growing sectors within the automotive industry.
3. One reason for this growth is the inclusion of additional restraint devices on vehicles.For example, the average number of air-bag modules has increased from one to two per vehicle in the early 1990s to four to six per vehicle for the latest models, with more expected to come.
4. Another reason for this growth is an increase in the complexity and sophistication of the safety systems' functional requirements.For example, to minimize out-of-position occupant injuries, a smart air-bag system needs to be equipped with occupant-sensing capabilities.
5. Particularly notable in the evolution of restraint systems has been the phenomenon of increasing use of electronics, which has occurred in parallel in the automotive world, as well as most technology fields.Upcoming products implemented in electronics, such as rollover and other sensors, are being added into an integrated vehicular safety system.