A seat belt, 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. As part of an overall occupant restraint 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) and by preventing the passenger from being thrown from the vehicle.
Until the 1980s, three-point belts were commonly available only in the front seats of cars; the back seats had 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 passenger safety regulations in nearly all developed countries requiring that all seats in a vehicle be equipped with three-point belts. Since September 1, 2007, all new cars sold in the U.S. require a lap and shoulder belt in the center rear.
Besides regulatory changes, "seat belt syndrome" has led to tremendous liability for vehicle manufacturers. One Los Angeles case resulted in a $45 million jury verdict against Ford Motor Company; the resulting $30 million judgment (after deductions for another defendant who settled prior to trial) was affirmed on appeal in 2006.
American physicians in the 1920s advocated the use of seat belts in cars. Some of them even outfitted their cars with seatbelts. Plastic surgeon Claire L. Straith and physician C. J. Strickland were at the forefront of that demand. Strickland founded the Automobile Safety League of America. The American public showed little interest.
Engineer Hugh De Haven invented the inertia reel and created the concept of "wearing" the car and "packaging" passengers.
Safety belts were tested by Col John P. Stapp, using a rocket sled and himself as the guinea pig, among others. His studies explained the phenomenon that most people injured or killed in plane crashes didn't die when the plane hit the ground, but when the person hit the inside of the plane.
Edward J. Hock invented the safety belt first used by the Ford Motor Company as standard equipment, while he was on active duty with the military as a flight instructor. In 1955 his idea was accepted by the naval authorities, and Hock was awarded $20.50 for his invention. The original schematic and blueprints shows that he utilized scrap parachute strapping to implement his idea. He was never awarded anything other than the $20.50 award, a letter of recognition, a picture with military "brass", and a newspaper article to his credit.
The three point seat belt (the so-called CIR-Griswold restraint) was patented in 1951 by the Americans Roger W. Griswold and Hugh De Haven.
Saab was the first car manufacturer to introduce seat belts as standard in 1958. After the Saab GT 750 was introduced at the New York motor show in 1958 with safety belts fitted as standard, the practice became commonplace.
In 1955 Ford offered for the first time lap belts as an option. In 1956, largely at the insistence of executive Robert McNamara, seat belts were offered for consumer automobiles within the "Lifeguard" safety package. The safety device was met with ridicule by others in the industry, but it caught on with the public. By 1964, Most U.S. automobiles were sold with standard front seat belts; rear seat belts were made standard in 1968.
In 1970, the state of Victoria, Australia, passed the first law worldwide making seat belt wearing compulsory for drivers and front-seat passengers.
The public service jingle, "Buckle Up for Safety", first heard in the 1960s, was taken from a song called "Buckle Down, Winsocki", from the 1943 musical, Best Foot Forward.
Most seat belts are equipped with locking mechanisms (or inertia reels) that tighten the belt when pulled fast (e.g. by the quick force of a passenger's body during a crash) but do not tighten when pulled slowly. This is implemented with a centrifugal clutch, which engages as the reel spins quickly. Alternatively, this function may be secured by a weighted pendulum or ball bearing: when these are deflected by deceleration or roll-over they lock into pawls on the reel.
Types of inertia reel type seatbelts:
NLR (No Locking Retractor): Commonly used in recoiling lap belts
ELR V (Emergency Locking Retractor - Vehicle sensitive): Single sensitive mechanism, composed of a locking mechanism activated in an emergency by deceleration or rollover of the vehicle. Thus, the seatbelt is sensitive to the vehicle's motion.
ELR VW (Emergency Locking Retractor - Vehicle and Webbing sensitive): Dual sensitive means a seatbelt retractor that, during normal driving conditions, allows freedom of movement by the wearer of the seatbelt by means of length-adjusting components that automatically adjust the strap to the wearer, with a locking mechanism that is activated by two or more of the following:
A recent study by McCoy & Chou (2007) from the Ford Motor Company (Safety Test Methodology, SP-2123) demonstrated that the standard inertia reel seatbelt does not stop the head from making contact with the interior of the roof on a standard rollover test in their dynamic ROllover Component test System (ROCS). Even with modern pre-tensioning devices the head contacts the interior of the roof and the neck suffers 'visible' compression.
Seatbelts in many newer vehicles are also equipped with "pretensioners" and/or "Webclamps".
As with adult drivers and passengers, the advent of seat belts was accompanied by calls for their use by child occupants, including legislation requiring such use. It has been claimed that children in adult restraints suffer lower injury risk than unrestrained children.
The UK extended compulsory seatbelt wearing to child passengers under the age of 14 in 1989. It was observed that this measure was accompanied by a 10% increase in fatalities and a 12% increase in injuries among the target population. In crashes, small children who wear adult seatbelts can suffer characteristic "seat-belt syndrome" injuries including severed intestines, ruptured diaphragms and spinal damage. There is also research suggesting that children in inappropriate restraints are at significantly increased risk of head injury, one of the authors of this research has been quoted as claiming that "The early graduation of kids into adult lap and shoulder belts is a leading cause of child-occupant injuries and deaths. As a result of such findings, many jurisdictions now advocate and/or require child passengers to use specially designed child restraints. Such systems include separate child-sized seats with their own restraints and booster cushions for children using adult restraints. In some jurisdictions children below a certain size are forbidden to travel in front car seats.
For pregnant mothers, the foetus is protected by a sac full of amniotic fluid. This sac is quite strong and the fluid inside acts like a cushion to protect the foetus. The sac is pliable so it can change shape to a certain degree. The proper use of a seat belt will divert the pressure points off the sac, and thus the foetus would only be minimally affected. The lap belt should be worn low over the pelvic bones and not against the soft stomach area. The shoulder belt should be worn across the chest. Both should be worn snugly.. RoSPA acknowledge that some expectant mothers are concerned about the lap belt riding up over the 'bump' but state that the seatbelt should be worn at all times. Several devices are commercially available to keep the lap belt down on the hips and away from the 'bump' including the CG-Lock.
In 1955 (as a 1956 package) Ford offered lap only seat belts in the rear seats as an option within the Lifeguard safety package. In 1967 Volvo started to install lap belts in the rear seats. In 1972 Volvo upgraded the rear seat belts to a three point belt.
It has been stated that in crashes, unbelted rear passengers increase nearly fivefold the risk of death for belted front passengers.
In North America and some other parts of the world, cars sold since the early 1970s have included a seat belt light on the dashboard, reminding the driver and passengers to buckle up. Originally, these lights were accompanied by a warning buzzer whenever the transmission was in any position except park if either the driver was not buckled up or, as determined by a pressure sensor in the passenger's seat, if there was a passenger there not buckled up. However, this was considered by many to be a major annoyance, as the light would be on and the buzzer would sound continuously if front-seat passengers were not buckled up. Therefore, people who did not wish to buckle up would defeat this system by fastening the seatbelts with the seat empty and leave them that way.
By the mid-1970s, auto manufacturers modified the system so that a warning buzzer would sound for several seconds before turning off (with the warning light), regardless of whether the car was started. However, if the driver was buckled up, the light would appear, but with no buzzer. New cars sold in the United States in 1974 and the first part of the 1975 model year were sold with a special "ignition interlock", whereby the driver could not start the car until the seat belt was fastened; however, this system was short-lived. While this system debuted in passenger cars in 1972, it wasn't placed in pickup trucks until 1976.
By the early 1980s, many automakers selling in the U.S. market had replaced the buzzer (along with all other buzzers for functions such as headlights-on) with a seatbelt warning chime, though for some models, this change was not implemented until the 1990s or even the early 2000s. Today, many of these carmakers use a red figure with its seatbelt on to serve as its seatbelt warning light, and it may stay on for several minutes after the car is started if the driver's seat belt is not fastened.
In Europe most modern cars include a seat-belt reminder light for the driver and some also include a reminder for the passenger, when present, activated by a pressure sensor under the passenger seat. In some systems (i.e. older Volvos), the seatbelt is connected to the turn signal relay, making clicking sounds constantly until the front passengers are buckled up.
Some newer cars from Audi, BMW, Ford, Honda, Hyundai, Mercedes-Benz, and Toyota will intermittently flash the reminder light and sound the chime until the driver (and sometimes the front passenger, if present) fasten their seatbelts.
This has led many countries to adopt mandatory seat belt wearing laws. It is generally accepted that, in comparing like-for-like accidents, a vehicle occupant not wearing a properly fitted seat belt has a significantly higher chance of death and serious injury. One large observation studying using US data showed that the odds ratio of crash death is 0.46 with a three-point belt, when compared with no belt. In another study, that examined injuries presenting to the ER pre- and post-seat belt law introduction, it was found that 40% more escaped injury and 35% more escaped mild and moderate injuries.
The effects of seat belt laws are disputed by some, stemming from the observation that following the passage of seat belt laws, road fatalities often did not decrease. There was also concern that instead of legislating for a general protection standard for vehicle occupants, laws that required a particular technical approach would rapidly become dated as motor manufacturers would tool up for a particular standard which could not easily be changed. For example, in 1969 there were competing designs for lap and 3-point seat belts, rapidly-tilting seats, inflatable restraints and air bags being developed. But as countries started to mandate seat belt restraints the global auto industry invested in the tooling and standardized exclusively on seat belts, and ignored other designs, such as air bags, for several decades
In one trial subjects were asked to drive go-karts around a track under various conditions. It was found that subjects who started driving unbelted drove consistently faster when subsequently belted. Similarly, a study of habitual non-seatbelt wearers driving in freeway conditions found evidence that they had adapted to seatbelt use by adopting higher driving speeds and closer following distances. Similar responses have been shown in respect of anti-lock braking system and, more recently, airbags and electronic stability control.
A 2001 analysis of US crash data aimed to establish the effects of seatbelt legislation on driving fatalities and found that previous estimates of seatbelts effectiveness had been significantly overstated. According to the analysis used, seatbelts were claimed to have decreased fatalities by 1.35% for each 10% increase in seatbelt use. The study controlled for endogenous motivations of seat belt use, which it is claimed creates an artificial correlation between seat belt use and fatalities, leading to the conclusion that seatbelts cause fatalities. For example, drivers in high risk areas are more likely to use seat belts, and are more likely to be in accidents, creating a non-causal correlation between seatbelt use and mortality. After accounting for the endogeneity of seatbelt usage, Cohen and Einav found no evidence that the risk compensation effect makes seatbelt wearing drivers more dangerous, a finding at variance with other research.