Seat belt
A seat belt, sometimes called a safety belt, is a harness designed to hold the occupant of an car or other vehicle in place if a collision occurs. Seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle or from being thrown from the vehicle. In cars seat belts also prevent rear-seat passengers from crashing into those in the front seats.
Lap belts are seat belts that go over the wearer's hips. These were an earlier style of belt and are today less common in the developed world, being found mostly in passenger aircraft. Shoulder belts, or three-point belts, include a lap belt and a second belt going from one anchor point on the lap belt to a point over and behind the occupant's shoulder. Three point harnesses were first made readily available in mass-produced vehicles by Volvo. Until recently shoulder belts were only available in the front seats of the cars, the back seats having only lap belts. Evidence of the potential for lap belts to cause separation of the lumbar vertebrae and the sometimes associated paralysis, or "seat belt syndrome", has led to a revision of safety regulations in nearly all of the developed world requiring that all seats in a vehicle be equipped with three-point belts.
Five-point harnesses are safer but more restrictive seat belts, typically found in child safety seats, and also in racing cars. The lap portion is connected to a belt between the legs and there are two shoulder belts, making a total of five points of attachment to the seat.
Seat belts were introduced in aircraft in the 1930s. However, they were not required by law in the US on passenger vehicles until the 1968 model year.
Mechanism
Seat belts are designed such that they tighten when pulled hard (in the event of a crash) but do not tighten when pulled slowly. See the page http://auto.howstuffworks.com/seatbelt.htm for more.
Legislation
The issue of seat belt legislation has been a source of some controversy. Hospital based studies of accident victims, experiments using both crash test dummies and actual human cadavers have indicated that wearing seat belts should provide a reduced risk of death and injury in many types of car crash. This has lead many countries to adopt mandatory seat belt wearing laws. It is generally accepted that, in comparing like-for-like accidents, a vehicle occupant wearing a properly fitted seatbelt has a significantly lower chance of death or serious injury.
However, the effects of such laws are hotly disputed. The dispute centres on the effects of seat belt legislation for both car occupants and non-vehicle occupants, such as motorcyclists, cyclists and pedestrians. The effect of seat belt laws influenced the development of the risk compensation hypothesis which argues that car drivers may adjust their driving behaviour adversely in response to the increased sense of personal safety wearing a seat belt provides.
de:Sicherheitsgurt
es:cinturón de seguridad
ja:シートベルト