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A three-point seat belt.

A safety belt , sometimes called a seat 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.

Use of seat belts by child occupants[]

Main article: Infant car seat

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.[1] In crashes, small children who wear adult seatbelts can suffer "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,[2] 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."[3] As a result of such findings, many jurisdictions now advocate 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.[How to reference and link to summary or text]

In rear seats[]

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.[4]

In crashes, unbelted rear passengers increase the risk of belted front seat occupants' death by nearly five times.[5][6]

Reminder chime and light[]

File:11 ceintures.jpg

In North America and some other parts of the world, cars sold since the early 1970s have included an audiovisual reminder system consisting of a light on the dashboard and a buzzer or chime reminding the driver and passengers to fasten their belts. 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 leaving 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.

Today, the belt warning light 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.

Some cars will intermittently flash the reminder light and sound the chime until the driver (and sometimes the front passenger, if present) fasten their seatbelts, and they sometimes even lock the speed to 10 km/h or less.


Main article: Seat belt legislation

Observational studies of car crash morbidity and mortality,[7][8][9] experiments using both crash test dummies and human cadavers indicate that wearing seat belts greatly reduces the risk of death and injury in the majority of car crashes.

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 and substantially 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.[10] 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.[11]

The effects of seat belt laws are disputed by those who observe that their passage did not reduce road fatalities. 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, 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 restraint designs such as air bags for several decades[12]

Risk compensation[]

Some have proposed that the number of deaths was influenced by the development of risk compensation, which says that drivers adjust their behavior in response to the increased sense of personal safety wearing a seat belt provides.

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.[13] 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.[14] Similar responses have been shown in respect of anti-lock braking system and, more recently, airbags and electronic stability control.[How to reference and link to summary or text]

A 2001 analysis of US crash data aimed to establish the effects of seatbelt legislation on driving fatalities[15] 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.

Increased traffic[]

Other statistical analyses have included adjustments for factors such as increased traffic, and other factors such as age, and based on these adjustments, a reduction of morbidity and mortality due to seat belt use has been claimed.[7] However, Smeed's law predicts a fall in accident rate with increasing car ownership and has been demonstrated independently of seat belt legislation.

Use in vehicles other than cars[]


Pros[16][17] and cons[18][19][20][21] had been alleged about the use of seatbelts in School Buses. See also Seat belts in school buses.


Use of seatbelts in trains has been investigated. Concerns about survival space intrusion in train crashes and increase of injuries to unrestrained or incorrectly restrained passengers led the researches to discourage the use of seat belts in trains.

It has been shown that there is no net safety benefit for passengers who choose to wear 3-point restraints on passenger carrying rail vehicles. Generally passengers who choose not to wear restraints in a vehicle modified to accept 3-point restraints receive marginally more severe injuries..[22]


The "Father of Crash Survivability", Hugh De Haven, was a plane pilot. His interest in crash survivability was sparked by him surviving a plane crash during the First World War.

See also[]


  1. Adams, John (1995). Risk, London: UCL Press Ltd. University College.
  2. Winston FK, Durbin DR, Kallan MJ, Moll EK (June 2000). The danger of premature graduation to seat belts for young children. Pediatrics 105 (6): 1179–83.
  3. "Kids at Risk: When Seatbelts are NOT Enough", by Karp H, Reader's Digest (US Edition), November 1999.
  4. Volvocars corporate website
  5. Ichikawa M, Nakahara S, Wakai S (January 2002). Mortality of front-seat occupants attributable to unbelted rear-seat passengers in car crashes. Lancet 359 (9300): 43–4.
  6. "Unbelted rear passengers 'biggest danger in crash"
  7. 7.0 7.1 Nakahara S, Ichikawa M, Wakai S (2003). Seatbelt legislation in Japan: high risk driver mortality and seatbelt use. Inj. Prev. 9 (1): 29–32.
  8. Allen S, Zhu S, Sauter C, Layde P, Hargarten S (2006). A comprehensive statewide analysis of seatbelt non-use with injury and hospital admissions: new data, old problem. Academic emergency medicine : official journal of the Society for Academic Emergency Medicine 13 (4): 427–34.
  9. Bourbeau R, Desjardins D, Maag U, Laberge-Nadeau C (1993). Neck injuries among belted and unbelted occupants of the front seat of cars. The Journal of trauma 35 (5): 794–9.
  10. Bédard M, Guyatt GH, Stones MJ, Hirdes JP (2002). The independent contribution of driver, crash, and vehicle characteristics to driver fatalities. Accident; analysis and prevention 34 (6): 717–27.
  11. Thomas J (1990). Road traffic accidents before and after seatbelt legislation--study in a district general hospital. Journal of the Royal Society of Medicine 83 (2): 79–81.
  12. includeonly>Fenton, John. "Safety Design", The Times, 1969-01024.
  13. Streff FM, Geller ES (1988). An experimental test of risk compensation: between-subject versus within-subject analyses. Accident; analysis and prevention 20 (4): 277–87.
  14. Janssen W (1994). Seat-belt wearing and driving behavior: an instrumented-vehicle study. Accident; analysis and prevention 26 (2): 249–61.
  15. 'The Effects of Mandatory Seat Belt Laws on Driving Behavior and Traffic Fatalities' by Alma Cohen and Liran Einav at Harvard Law School
  16. Spital M, Spital A, Spital R (November 1986). The compelling case for seat belts on school buses. Pediatrics 78 (5): 928–32.
  17. Albers AC (2001). Should there be laws mandating seatbelts in all school buses? Writing for the pro position. MCN Am J Matern Child Nurs 26 (1): 8.
  18. Begley CE, Biddle AK (1988). Cost-benefit analysis of safety belts in Texas school buses. Public Health Rep 103 (5): 479–85.
  19. Seat-belts in School Buses?
  20. Pros, Cons of School Bus Seatbelts
  21. Garzon DL (2001). Should there be laws mandating seatbelts in all school buses? Writing for the con position. MCN Am J Matern Child Nurs 26 (1): 9.
  22. Assessment of three-point passenger restraints (seatbelts) fitted to seats on rail vehicles PDF, page 33

External links[]

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