Seat belt legislation

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Seat belt legislation is a law or laws put in place to enforce or require the wearing of seat belts while driving, or a passenger in, a vehicle. Most western countries have compulsory seat belt laws.

Contents

1 Predicted effects
2 Measured effects

2.1 Non-vehicle occupants
2.2 The British Law

3 Support for seat belt legislation
4 Current position

4.1 United States
4.2 Developing countries
4.3 Dilution of risk compensation effect

5 Seat belt legislation around the world
6 Summary
7 See also
8 External links
9 References and Further Reading
10 Notes

Predicted effects

The move towards seat belt legislation started in Australia in the late 1960s, although it was echoed elsewhere. It was influenced primarily by doctors working in emergency medicine, who noted that seat belt wearers were less likely to be seriously injured in collisions^{[[Citing sources citation needed]]}.

Hospital based case-control studies of crash victims supported the empirical observation that those wearing seat belts were less likely to be killed or seriously injured than those not wearing them. Based on this type of study, predictions such as 45% reductions in fatal injury and 50% reductions in moderate-to-critical injury were made^{[[Citing sources citation needed]]}. Experiments using both crash test dummies and actual human cadavers also indicated that wearing seat belts should lead to reduced risk of death and injury in certain types of car crash.

As a result of such predictions the use of seat belts by vehicle occupants was made compulsory in Victoria, Australia in 1970, followed by the rest of Australia and other countries during the 1970s and 1980s. Predicted savings of lives in the thousands or (in the case of the USA) tens of thousands have been the standard currency of seat belt legislation proponents.

Measured effects

Initial reports from Australia indicated that the laws had indeed been effective: a rising trend in fatalities pre-1970 had been arrested and reversed, and this was attributed to the effect of seat belt legislation. But this did not meet with universal acceptance: introduction of early seat belt laws coincided with the world oil crisis, and it was evident that road casualties had dropped in all countries, not just those with seat belt laws (an identical reversal of trend is visible in the UK at the same time[Department for Transport], Transport Statistics. although British seat belt legislation was not introduced until a decade later). Claims of lives saved based on extrapolation of trends pre-law would therefore be skewed by the effect of the oil crisis, which resulted in all countries in reduced miles travelled and reductions in speedsAdams, J: Risk, 1995, Routledge, ISBN 1857280687.

When a seat belt law was proposed in the UK, similar claims for potential lives and injuries saved were advanced. William Rodgers, then Secretary of State for Transport, stated that:

Professor John Adams of University College London was sceptical of such claims and set out to analyse the effect of seat belt laws as then in force and assess how well they matched predictions. His findings were published in 1981 (and can be found in the Society of Automotive Engineers transactions of that year.[SAE transactions].

His conclusion was that in the eighteen countries surveyed, accounting for approximately 80% of the world's motoring, those countries with seat belt laws had fared no better, and in some cases (e.g. Sweden, Ireland and New Zealand) significantly worse than those without. In particular, those outside cars (pedestrians and cyclists) had experienced significant increases in fatalities involving cars. In response the UK's Department of Transport commissioned a study on the effects of seat belt laws in Sweden, West Germany, Denmark, Spain, Belgium, Finland, the Netherlands and Norway. This study, known as "the Isles report" after its author, used the United Kingdom and Italy as controls for no-law countries compared casualty trends for both those inside and outside cars between law and no-law states. The report predicted that, based on the experiences of the eight countries studied, a UK seat belt law would be followed by a 2.3% increase in fatalities among car occupants.

In order to explain this disparity, Adams advanced the hypothesis that Protecting car occupants from the consequences of bad driving encourages bad driving. Subsequent analysis has suggested that a number of mechanisms are in play:

Better protected drivers take less care (risk compensation or risk homeostasis).
Case-control studies based on voluntary use of safety aids can attribute to the aid benefits that actually come from the risk-averse nature of those likely to use them voluntarily (confounding), particularly early adopters.
Fatality rates are subject to considerable stochastic noise and comparison of single years or short periods can be misleading.

There is evidence to support the risk compensation theory. In one experiment^{[[Citing sources citation needed]]}, two groups of drivers (habitual wearers and habitual non-wearers) were asked to drive a test track under the guise of testing different seat belt materials for comfort. It was observed that the habitually unbelted drivers consistently drove faster and cornered faster when wearing seat belts. Similar effects have been observed in respect of other interventions such as anti-lock brakes. In another, taxi drivers who were habitual non-wearers were timed over a route with passengers who did, and others who did not, insist on the dirver wearing a belt. They were observed to complete the route faster when belted.[Wilde, Target Risk]

Non-vehicle occupants

From the very beginning in AustraliaEvaluation of Automobile Safety Regulations: The case of Compulsory Seat Belt Legislation in Australia. by J.A.C. Coneybeare, Policy Sciences 12:27-39, 1980, and subsequently New ZealandCompulsory Seat Belt Use: Further Inferences, by P. Hurst Accident Analysis and Prevention., Vol 11: 27-33, 1979, there had been indications that seat belt laws might produce increases in deaths and injury among those outside cars such as motorcyclists, cyclists and pedestriansSource: Department for Transport, Road Accidents Great Britain . The author of the Isles report was alarmed to find that in Europe the predominant effect of seat belt legislation was of increased numbers of injuries to non-car users. The author predicted that in the UK, deaths to other road users would rise by approximately 150 per year in the event of compulsory seat belt wearing legislation. In terms of injuries to other road users the prediction was for a 11% increase in pedestrian injuries with injuries to other road users climbing by 12 to 13% (numerically 7,000 and 36,000 respectively).

The British Law

The Isles report was never published (according to some authoritiese.g. Davis R. Death on the Streets, ISBN 0948135468, 1992. it was suppressed as it did not back the pre-existing position of Government and the Department), and is known mainly because it was leaked to The Spectator magazine some time after the law was passed. A law was passed which at the same time introduced evidential breath testing.

The law mandating the compulsory wearing of seat belts for front seat occupiers came into force on January 31, 1983 in the UK.

In the two years following the law there were increases of 14% in pedestrian deaths, 40% in cyclist deaths and 27% in rear passenger deaths, somewhat in excess of Isles' predictions. There was a reduction in driver fatalities and an increase in fatalities of rear passengers (not covered by the law)Durbin J, Harvey A: The effects of seat belt legislation on road casualties in Great Britain, DtP, October 1985. A subsequent study of 19,000 cyclist and 72,000 pedestrian casualties seen at the time suggests that seat belt wearing drivers were 11-13% more likely to injure pedestrians and 7-8% more likely to injure cyclists Source:Methodological Issues in Testing the Hypothesis of Risk Compensation by Brian Dulisse, Accident Analysis and Prevention Vol. 25 (5): 285-292, 1997. In January 1986 an editorial in The Lancet noted the shortfall in predicted life-saving and "the unexplained and worring increase in deaths of other road users"Lancet, 11 January 1986, p75. Shortly after this, legal compulsion was extended indefinitely.

Analysis of fatality figures before and after the law shows:

a clear increase in pedestrian, cyclist and rear-passenger fatalities in collisions involving passenger cars
no such increase in casualties in collisions involving buses and goods vehicles, which were exempt from the law
a reduction in the number of drivers found to be drunk at the scene of collisions
a reduction in overall fatalities between the hours of 10pm and 4am (peak hours for drink-driving offences)
no reduction in overall fatality rates outside these hours.

In analysing these results, Adams concludes that there is no evidence of the seat belt law having reduced overall fatality numbers, and that there is evidence of fatalities having migrated from drivers to vulnerable road users. Although the Government argued at the time that the law had saved lives, it has subsequently attributed almost all the benefit for the small reduction in overall driver fatalities to the introduction of evidential breath testing.

Seat belt use is a binary: the belt is either worn or not. Belt laws, which tend to lead to substantial changes in wearing rates over very short periods, would, if the predictions of up to 50% reductions in fatalities are correct, be expected to demonstrate large scale step changes in fatality figures. No such changes have been observed. Whether seat belts reduce fatalities, it is inescapably true that any reductions fall well below the predicted levels, a fact widely interpreted as supporting risk compensation theory.

Support for seat belt legislation

Other authorities claim that seat belt legislation has reduced the number of casualties in road accidents. For example, this [statistical analysis] by the NHTSA claimed that seat belts save over 10,000 lives every year in the US. The FARS further writes: [link]

"Research on the effectiveness of child safety seats has found them to reduce fatal injury by 71 percent for infants (less than 1 year old) and by 54 percent for toddlers (1-4 years old) in passenger cars. [...] Among passenger vehicle occupants over 4 years old, safety belts saved an estimated 11,889 lives in 2000."

However, these figures for lives saved are obtained by extrapolating experimentally derived estimates for seat belt effectiveness to the entire population based on recorded seat belt use and recorded crash rates; this is problematic for the reasons noted above and it is argued that this is an example of begging the question: such evidence cannot of itself provide evidence of actual reductions in deaths that might be reasonably attributed to seat belts.

In Victoria, Australia use of seat became compulsory in 1970. By 1974 decreases of 37% in deaths and 41% in injuries, including a decrease of 27% in spinal injuries, were observed, compared with extrapolations based on pre-law trends. The Victorian legislation coincided with the oil-crises of the early 1970s, a time when traffic injuries and deaths fell in most industrialised countries. Adams' analysis shows Victoria's injury trends as being above the average for all industrialised countries.

Current position

United States

Recently there has been a push for seat belt laws in the United States. As elsewhere, this has resulted in controversy. In addition to the above observations in respect of the measured effect of seat belt laws, the debate in the US has highlighted some other comments which received less attention in other countries.

In USA, seatbelt legislation is left up to state governments. Depending on which state you are in, not wearing a seatbelt is either a primary offense or a secondary offense. Primary offense meaning a police officer can pull you over for the seatbelt law violation alone, and secondary offense meaning you can only be punished for the seatbelt law violation if you're already pulled over for another reason. States with primary seatbelt laws are often referred to as "Click-it or ticket" states. As of July 2004, 21 states have primary seatbelt laws and 28 have secondary seatbelt laws. The exception being New Hampshire, which does not have a seatbelt law for persons aged 18 and over.

One facet of the US case is speculative consideration of effects on car occupants (e.g., the possibility that seat belt use can cause internal, neck and spinal injuries as it leaves the head free to move inertially while the rest of the body is restrained), and may trap an occupant in a vehicle. However, proponents of seat belts claim that the benefits in injuries saved far outweigh these risks, and do not credit the idea that they prevent occupants from escaping the car (and also claim that in any case being thrown from the vehicle is much more likely to result in death than being restrained within it).

It is valid to consider the issue of rotational injury to the brain, causing diffuse axonal injury, a leading cause of persistent vegetative state, but there is little credible evidence to support the idea that this is positively associated with seat belt use and considerable evidence to support the idea that head injuries are much more likely to happen, and to be severe, in unrestrained drivers.

Many US opponents also object on the grounds that seat belt laws infringe on their civil liberties. This is accorded much higher priority in the US than in some other countries.

Developing countries

It might be argued that the risk posed to vulnerable road users is of less importance where walking and cycling are relatively insignificant, as they are in the US. In many developing countries, however, pedestrians, cyclists, rickshaw operators and moped users represent the majority of road users. These countries rarely have the resources to physically separate such road users from car traffic (an idea which is itself arguably inequitable, given that those forced into second-class facilities are not the ones posing the danger). In many such countries non-car occupants also represent the majority of road fatalities. Some believe such countries face a serious moral dilemma about importing "Western", "car-centered", models of "road safety" such as compulsory seat belt legislation.

Dilution of risk compensation effect

There is very little literature considering how risk compensation effects, subjective as they must be, change over time. Although there is good evidence that habitually unbelted drivers will take more risks when belted, and that habitually belted drivers will be more cautious when unbelted, by the nature of laws, new drivers will be habituated from the outset. An interesting footote to the debate is analysis by Adams of the relationship between accident records and car ownership, a relationship known as Smeed's law ([link]). It appears that this empirical rule relating car casualties to the level of car ownership has continued to hold across several decades of safety interventions, including seat belt laws. It may be that modern drivers, habituated from the outset to seat belt use, are also habituated from the outside to greater expectations of car performance: faster cornering, faster acceleration, later braking. Alternatively it may be that improvements are due to the increasing profile of safety interventions as car ownership increases, whatever the country, as road safety professionals prefer.

Seat belt legislation around the world

This section gives an overview of the years in which seat belt legislation was first introduced in various countries around the world, this includes both regional and national legislation.

Country Compulsory for Must be fitted in Sources

Driver Passenger Back seats Bus passengers Cars Busses
Australia 1970 [link]
EU 1993 [link]
France 1973 (outside cities), 1975 (cities at night), 1979 (all) 1990 2003 1979 [link] [link]
Germany 1976 1976 1984 1999 1970, 1979 (back seat) 1999 [link]
Ireland 1979
Hungary 1976 1993 [link]
Italy
Japan 1969 [link]
New Zealand 1979 [link]
Spain
Sweden 1969 [link]
Switzerland
UK 1983 1989 (children), 1991 (adults) 1997 1987 2001 [link]
U.S. 1994 1994 1994 2004 [link]

Country	Compulsory for	Must be fitted in	Sources
Driver	Passenger	Back seats	Bus passengers	Cars	Busses
Australia	1970						[link]
EU	1993				[link]
France	1973 (outside cities), 1975 (cities at night), 1979 (all)	1990	2003	1979		[link] [link]
Germany	1976	1976	1984	1999	1970, 1979 (back seat)	1999	[link]
Ireland	1979
Hungary	1976		1993				[link]
Italy
Japan					1969		[link]
New Zealand					1979		[link]
Spain
Sweden					1969		[link]
Switzerland
UK	1983	1989 (children), 1991 (adults)	1997	1987	2001	[link]
U.S.	1994	1994	1994			2004	[link]

Summary

Seat belt legislation is an interesting case-study in safety intervention. What appears at face value to be a simple and valid inference, that comparisons between those who do and do not use a safety aid voluntarily can be scaled to predict benefits for an entire population subject to compulsory use of that aid, has been shown to be flawed. The same flawed reasoning has been used to support other interventions such as bicycle helmets, with similarly contradictory results.

Whether seat belt laws save lives is still disputed. Arguably any risk compensation effect might be diluted or disappear altogether over time as belt use becomes the norm, and trends in motor casualties are undoubtedly favourable (although some put this down to Smeed's law). There is little dissent, though, from the view that any actual savings fall well short of the numbers predicted by simple extrapolation, and it was these predictions which led to the laws being passed. Whether or not laws would have been passed based on much more modest reductions, accompanied by rises in fatalities for vulnerable road users, is debatable.

External links

Links to sites/studies that endorse seat belts

Links to sites/studies skeptical/critical of seat belt legislation

References and Further Reading

John Adams, 1995, Risk, Routledge, ISBN 1857280687 — Authoritative reference on risk compensation theory.

Wilde G.S. Target Risk PDE Publications, 1994

The Isles report "Seat belt savings: Implications of European Statistics", UK DoT, 1981, Sourced from Death on the Streets, Cars and the Mythology of Road Safety by Robert Davis, Leading Edge Press, North Yorkshire UK, 1992 and "Report questions whether seat belts save lives" by M. Hamer, New Scientist, 7 February 1985 p7

Evaluation of Automobile Safety Regulations: The case of Compulsory Seat Belt Legislation in Australia. by J.A.C. Coneybeare, Policy Sciences 12:27-39, 1980

Compulsory Seat Belt Use: Further Inferences, by P. Hurst Accident Analysis and Prevention., Vol 11: 27-33, 1979

Wilde G.S. Risk Homeostasis and Traffic Accidents Propositions, Deductions and Discussion of Dissension in Recent Reactions, Ergonomics 1988 Vol, 31, 4:439

Methodological Issues in Testing the Hypothesis of Risk Compensation by Brian Dulisse, Accident Analysis and Prevention Vol. 25 (5): 285-292, 1997

RS 255 The initial impact of seat belt legislation in Ireland by R. Hearne, An Foras Forbatha, Dublin, 1981

The efficacy of seat belt legislation: A comparative study of road accident fatality statistics from 18 countries, by J. Adams. Department of Geography University College, London 1981

Casualty Reductions, Whose Problem? By F. West-Oram, Traffic Engineering and Control, September 1990

The Puzzle of Seat Belts Explained, Press Release of the Annual Conference of the British Psychological Society, April 1999

Reconsidering the effects of seat belt Laws and Their Enforcement Status by T.S. Dee Accident Analysis and Prevention., Vol 30(1): 1-10, 1998

Notes

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