• No results found

that had not.5 6None of the countries except Australia had shown a change in death rates in the years after

N/A
N/A
Protected

Academic year: 2021

Share "that had not.5 6None of the countries except Australia had shown a change in death rates in the years after"

Copied!
5
0
0

Loading.... (view fulltext now)

Full text

(1)

Journal of Epidemiology

The

benefit

of

Kingdom

seat

belt

legislation

in

the United

MARK McCARTHY

From theDepartment

of

Community Medicine, University College, London.

ABSTRACr Legislation for compulsory wearing ofseatbeltsby cardriversand front seatpassengers has been acclaimed as a major public health advance. Reports from other countries,and tworecent evaluative studies inthe United Kingdom, have suggested that legislation reduces both deaths and injuries. To assess the effect of the UK law5years after itsimplementation, trends inroutine datafor 1976-1987 have beenreviewed. There were two sources of data: mortality statistics, published by the Office of Population Censuses and Surveys in the quarterly Monitor DH4, and road accident statistics, recorded by the police and published by the Department ofTransport. There is a downward

trend

in

deaths

overthe

period,

but the data show little impact from the law. One explanation for this

lack of effect

is the risk compensation hypothesis, which suggests that "safety" improvements are transferred

by

drivers into increasedperformance-the amount and speed of travel. Public health

policies

need to take into account the complex behavioural interactions between travel andsafety choices ifthey are to affect underlying trends.

Evidence that wearing 3-point seat belts saves lives and reduces injurieswas reviewed by theTransport and Road Research Laboratory in 1979.' Eight studiescomparing the injuries of belted and unbelted vehicle occupants had found reductions in serious injuries of around 60%, andone study of fatal car accidents in Britain had estimatedthatwearingseat belts would halve the number of deaths. The report noted thatseatbeltlawsexisted in 15countries, but reliedprimarilyonevidence fromAustralia,where the state of Victoria had introduced legislation in December1970.Thereportstated:"TheVictoria data suggestthatseatbelts,when worn,reduced the riskof death byatleast40 percent."3

During the parliamentary debate on seat belts in 1979, the Secretary ofStateforTransport,MrWilliam Rogers, stated: "Compulsioncould saveup to 1000 lives and 10 000injuriesa

year."2

Aleadingarticle in the British Medical Journalproposedfivecourses of

governmentactionto reduceroadaccidents,and, as

toppriority, claimed that "thecase forseatbelts is overwhelmingand

urgent."3

A lawcompelling cardriversand their front seat

passengers towear seat belts was finally passed by

parliament in July 1981, and introduced from February 1983. For the final House of Commons debate,thePresidents ofthreeRoyalMedicalColleges sent alettertoParliamentexpressing"despairatthe failureofourlegislatorstotakesimplestepstoreduce

this annual carnage."4 Opposition to seat belt legislation, especially within the majority Conservativeparty,mainlycamefromMPsconcerned that legislation would encroach upon "individual freedom".

However, astudy publishedin1981, andmentioned in the Parliamentarydebate,had comparedthetrend in road accident deaths during the 1970s in 13 countries that had broughtin seatbelt lawswith four thathadnot.5 6Noneofthecountriesexcept Australia hadshown a change indeathrates inthe years after legislation, and, takentogether, the countries without legislation(Britain,Italy, Japan and the United States) hadalarger fallindeathratesthan thoseintroducing seatbelt laws.Respondingtothisreport, a statistician attheDepartmentofTransport looked at theeffects of seatbelt laws in eightWestern Europe countries, and came to much the same conclusions. However, this report, dated April 1981, was not brought to

parliament's attention by the Minister during the debate,and itsexistenceonlycametolightinFebruary 1985.7

Thegovernment supported twoevaluations of the effect ofthe seat belt law. The firststudy,fundedby theDepartment ofHealth, wasinitiatedby a Belfast casualtysurgeon. Datawerecollected from 14hospital accident departments throughout the United Kingdom (excluding the London area) for 1 year before and 1 year after the introduction of the

(2)

the UnitedKingdom legislation.8 Casualty officers recorded details of patientsattendinghospital accident departments for road traffic accident injuries. There was a 15% reductioninpatients arrivingatthe 14hospitals,and proportionately fewer patients with severe injuries (observationsonthe severity ofinjurieswere made by casualty officers). Therewere fewer eye injuries and major fractures, but more injuries to abdominal organs. Brain injuries to drivers also increased. A parallelstudy of deaths, based on coroners'records, wasinconclusive.8

The second study was contracted by the Department of Transport to two experienced academic mathematicians, who used time-series models of deaths and "killed and serious injuries" (KSI) datatocomparetheprevious 13 yearswith the 23 months after the law.9 There were significantly

fewer killed and seriously injured drivers and front seat passengers, but no change for rear seat passengers,cyclists and pedestrians.Fordeathsalone, the reduction in drivers and frontseatpassengerswas less, while deaths of other road users were substantially greater than expected. The authors estimated thatthe seat belt lawhad saved less than200 livesayear.

In1986, after3yearstrial, Parliament madethe seat belt lawpermanent. Data are nowavailabletoreview thepublic health effect of the lawoverthe5yearssince itintroduction.

Methods

Data onroadaccident deaths andinjuriesarecollected by threesources: the Office of Population Censuses and Surveys (OPCS); the Department of Transport; and the Department of Health.

OPCS records road accident deaths up to 1 year afteranaccident. Beingbased on coroners' verdicts, these data take longer to be notified than police reports at thetime oftheaccident, but, for the same reason, theyaremore accurate and morecomplete. The data are published annually in statistics series MB4. Since 1977 OPCS has published a quarterly Monitor(DH4) of deaths from accidents and violence which divides road accidents according to the dead person's mode of travel. Road accidents show monthlyvariations, rising in the winter monthsand

fallingto lower levelsin thespring, so anaverageis best shownbyannualfigures.

TheDepartmentofTransport publishesareporton roadaccidentsannually which also includes tables by road user, as well as numbers of accidents and casualties. Casualties are divided into minor and severe: severity is rated subjectively by individual police shortly after the accident.A"severe" accident canrangefromabrokenfingerto apatientadmitted

to an intensive care ward, but "generally will not includetheresults of a medicalexamination.""

Athirdpotentialsourceofdata about road accident

injuries is the Hospital Inpatient Enquiry (HIPE), publishedonbehalf of theDepartment ofHealthby

OPCS.However,in contrasttotheICD code used for deathcertification, HIPEdoes not code accidentsby the external cause of injury, only by the accident diagnosis.It isthereforeimpossiblefrom this sourceto

make a reliable estimate of hospital deaths and

discharges from road accidents alone. Data about home accidents are collected (by the Departmentof Trade) from a national sampleofhospital accident

departmentattendances,but there are no routine data onroadaccidents collected incasualtydepartments. Time series for the period 1976-87 have been constructed for deaths from the DH4 monitors. Similar series were gathered for deaths and injured from theDepartmentofTransport's publisheddata, along with asummary series on population, vehicle licences,accidents andcasualtiessince 1926. Results

Figure 1 shows data on road deaths reportedbythe police from 1976 to 1987, using the Department of Transport's categories of road user. Thedownward trendfrom 1976 forpedestrian and "other" roadusers (ie, motor vehicles) is evident, with a lesser fall in deaths of motorcyclists and little change for pedal cyclists.The"other" category showsamarked fallin the year after introduction ofcompulsory seat belt wearing,butthis can also be seen as variationwithin thedownwardtrend.

3000] 2500 2000-m 1500 1000' 500 Law

I

Others Pedestrian Motorcycle A,

* ^

*-

^

*

Pedalcycle 1975 1977 1979 1981 1983 1985 1987 Year

Fig I Casualtieskilledfrom road accidents, Great Britain 1976-87

(3)

Road accident deaths recorded by OPCS in England and Wales for 1976-87 are shown in fig 2,

usingalog scaleso astoincludeatrendfor all deaths.

Datafor 1981aremissing because of the strike by local

registrarsof deaths. In 1983 therewas amodest fall in

deathsofmotorvehicle drivers andmotorcyclists, and

to a lesserextent motorvehicle passengers, but this waspartially offset byarise in deaths of pedestrians

and pedal cyclists. From 1985 motorvehicle drivers andpassengerdeathswererising again. Theneteffect

onall road deathswas a slow downward trend.

10 000-(A X 1000 a Law AIldeaths Pedestrian _ MVDriver MV Passenger Motorcycle

c1 --I Pedalcycle

1001 . . . 1 1975 1977 1979 1981 1983 1985 1987

Fig 2 Road accidentdeaths, England& Wales 1976-87

Figure 3 shows police data at5 yearintervals for

Great Britainfrom1926,when statisticsbyroaduser were first recorded. The population has risen slowly

from 44 million in 1926to55 million in 1986. Vehicle licences (asaproxyforexposure)rosesteeply, but with aflatteningcurvesince the mid sixties. Casualtiesand

accidentsrose before, and again after,thewar(data

for thewaryears arenotavailable). Theyreached a

peak in the 1960s, and have slowlyfallen since then.

The number ofpeople killed ontheroads in 1927

(total 5125) is remarkably closetothenumber killed in 1987 (total 5329). The proportions have altered by road user: there are many more deaths of people

within motor vehicles (described in the table as

"others"),and falls inpedestrians, pedal cyclistsand

motorcyclists. Data onexposurearenotreported. Discussion

Avery," ina BritishMedical Journal leading article 1 year after compulsory car front seat belts were

introduced, claimed the lawas"aremarkablesuccess

storyin roadsafety legislation...asavingof350lives

108. 107 (A E 106. z 105 - Population AllMV licences 4_: Casualties Accidents

1041

' 1921 1931 1941 1951 1961 1971 1981 Year

Fig 3 Population, roadlicences, accidents and casualties, S-yearly, GreatBritain1926-86

and 4500 serious injuries". He recommended new

legislation for compulsory wearing ofrearseat belts. When the Casualty Surgeons' study8was published,

Mackay, in thesameJournal, claimed that the lawwas

saving about 400 livesayear,andwas"onethemost

successfulpieces ofpublic health legislation ever".12 Yet the evidence from routine data is not as

compellingas thesecommentariessuggest.

Table Roadvehicles, accidentsandcasualties,GreatBritain 1927and1987.

1927 1987

Population (millions) 44-0 554

RoadVehicles(millions) 19 22-2

Accidents(thousands) 134 239 Killed Pedestrians 2774 1703 Pedalcyclists 644 280 Motorcyclists 1175 723 Others 736 2419

Allkilledandinjured (thousands) 154 311 Source: Department of Transport. RoadAccidents Great Britain

1987. London:HMSO,1988(table 2).

What are the limitations to the two published

official evaluative studies? The Casualty Surgeons'

study8

useddata for 1 year before and 1 year after the seatbelt law wasintroduced. Moreover, itonlylooked at cardrivers and theirpassengers: it excluded other vehicle

drivers,

motor cyclists, pedal cyclists and

(4)

The benefit of seat belt legislation in the UnitedKingdom pedestrians. Thus itcould not estimate whether the legislation had been offset by any increase in road accident injuries for non-car-users. The interrupted time series modelofHarveyandDurbin9 usedalonger period before the law (13 years), weighted for proximity. Butthe post-lawperiod, less than2years, was short, given the seasonalperiodicityofthe data. An effect of the lawwas found with the killed and seriouslyinjured(KSI)data,butthe results for deaths alonewereequivocal.

ATransportand Road ResearchLaboratorystudy haslookedatthe reliability of non-fatal injury data recordedby the police. Theseverity of3641 patients attendingasingle hospital accidentdepartmentduring 1 year werecompared using theMinistryofTransport (MOT) injury classification and the Abbreviated Injury Scale

(AIS).13

The MOT "serious" injuries ranged on the AISfromminor(scalepoint 1) to critical (scale point5). Moreover,nearly30%ofthecasualty attenderswerefoundnot tohave beenreportedtothe police, with the highestnon-reportingrateinseriously injuredcyclists. Police datamaybetoounreliable for epidemiological conclusions.

Fewepidemiological studies showa simple cause-effect relationship between mortality trends and a single environmentalchange,especiallyinpreventive interventions. G SWilde, an American psychologist, hassuggested that "risk homeostasis"mayexplainthe lackofimpact ofthe seatbeltlaw.'415Wildeargues thatcomplex socialsystemsadjustto changedlevels of risk in accident and other public health settings. Adams proposes a more testable version of this hypothesis, "risk compensation".6 Harvey and

Durbin9

recognised the possibility of risk compensation intheir analysis: "The figures for KSI casualties lead one to reject the risk compensation hypothesis. On the other hand, the killed figures do lendsupport to the hypothesis".

Riskcompensationsuggests that whendrivers feel safer, they may take on a new level of driving behaviour(eg,drivingmoreaggressively), adjustingto their individual levelofrisk. They may alsoincrease theirriskexposureby drivingfurther.Becauseserious accidentsareso rare toanyindividual, this population change is imperceptible, but changing behaviour is clearly seen over time, for example, with improvements in car roadholding andperformance. Risk compensation is an important alternative to simple mechanistic models ofroadsafety.AsAdams suggests, thepublic health objectiveofgreatersafetyis cancelled out by the transport objective of more travel-more cars, morejourneysandgreaterspeed. Thepotential benefits of road "safety"improvements areconsumed asperformance benefits.

Risk compensation can also be accompanied by redistributionof risks. This may beevidentin theroad

deathstatistics: in Great Britain in theyearafter the law,therewas afallin deaths forcardrivers and front seat passengers, but a rise in deaths for rear passengers, cyclists and pedestrians. In subsequent years these small changes have evened out and the longer term trend for all road deaths continued. Redistribution of risksalso means that"safety"must

include an estimate of exposure. As Adams has commented,wehave fewer child road deathsnow not

because the roads are "safer" but because fewer children play in the roads.6 Equally, the long term

trend of falling pedestrianorcyclist deathsmayreflect the factthat,yearbyyear,thesetwogroupsofusers have been increasingly forced off the roads.

Whether risk compensation is an adequate explanation of driving behaviour and road safety remainsopen todebate. Manypeople resist theidea, since it dampens enthusiasm for simple, "obvious" policy interventions; but they must recognise the possibility that mechanical "safety improvements" (protection within cars, limitation of pedestrian access) are being translated into improved performance(higheraveragespeeds, fastercornering). Research needs to address the causes of the larger underlying trend offalling deaths and serious injuries inBritain since the1960s. We cannot expecteithercar manufacturers, or their customers, the drivers, to welcome "safety" measures that seriously impede individual transport performance. Public health legislationwill have toconsiderthe balance between publicrisk andindividual benefitsintransport as in otherareas.

Address for correspondence and reprints: Mark McCarthy, FFCM, MRCP, Department of Community Medicine, University College London, 66-72 Gower St, LondonWC1E6EA.

References

IAnonymous. The protection afforded by seat belts.

Crowthorne:Transport and Road ResearchLaboratory, 1979(supplementary report449).

2 RodgersW.Hansard 22March 1979, col 1720.

3Anonymous.Prioritiesinroad accidents.BrMedJ1979;i:

287-8.

4LeichnerH.Lives, liberty andseatbeltsinBritain:lessons for the United States.Int J Health Serv 1986; 16: 213-26.

Adams JGU. The efficacy of seatbelt legislation: a

comparativestudy of road accident fatality statistics from 18 countries. London: Department of Geography, University College London, 1981.

6Adams JGU. Risk and freedom. Cardiff: Transport Publishing Projects, 1985.

7 Hamer M.Reportquestions whetherseatbelts save lives. NewScientist 1985,7February (no 1442): 7.

8Rutherford WH, Greenfield T, Hayes HRM,Nelson JK.

The medicaleffectsofseatbeltlegislation in the United Kingdom. London: HMSO 1985 (DHSS Office ofthe

(5)

222

9HarveyAC,Durbin J. Theeffectsofseatbelt legislationon

British roadcasualties: a case study in structural time

series modelling. JRStatistSoc A 1986; 149: 187-227.

10Department ofTransport. Road accidents Great Britain 1987. London: HMSO, 1988.

"AveryJG.Seat beltsuccess:where next? Br MedJ1984;

288: 662-3.

12MackayM.Seat belts and riskcompensation.BrMedJ

1985; 291:757-8.

13Hobbs CA, Grattan E, Hobbs JA.Classification of injury severity by length of stay in hospital. Crowthorne: Transport and Road Research Laboratory,1979(TRRL Laboratory Report 871).

4Wilde GJS. The theory of risk homeostasis: implications forsafety and health. Risk Analysis 1982;2: 209-25.

15 Wilde GJS. Risk homeostasis theory and traffic accidents: propositions, deductions and discussionof dissension in recentreactions. Ergonomics 1988;31:441-68.

References

Related documents

To that end, the Open Travel Alliance (OTA) was formed in 1998 and now has a global membership of over 150 travel companies from suppliers, such as airlines, hotels, car rental, rail,

The anti-inflammatory activity of the title compounds (4a-f) and the parent compound AMACs (3a-f) were evaluated using inhibition of heat-induced albumin denaturation

19% serve a county. Fourteen per cent of the centers provide service for adjoining states in addition to the states in which they are located; usually these adjoining states have

Abstract The Research Data Centre (FDZ) of the German Federal Employment Agency (BA) in the Institute for Employment Research (IAB) was founded in 2004 and is intended mainly

It was decided that with the presence of such significant red flag signs that she should undergo advanced imaging, in this case an MRI, that revealed an underlying malignancy, which

Also, both diabetic groups there were a positive immunoreactivity of the photoreceptor inner segment, and this was also seen among control ani- mals treated with a

Field experiments were conducted at Ebonyi State University Research Farm during 2009 and 2010 farming seasons to evaluate the effect of intercropping maize with

After being exposed to a series of memory strategies for a period of 10 weeks, it was evident that most learners in the experimental group benefited from the intervention and showed