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. 2001 Jan 6;322(7277):50.
Reducing speed limit to 20 mph in urban areas
Evidence based principles should be applied to non-health sector interventions
Editor—Pilkington supports a reduction in traffic speeds to 20 mph (32 kph) on the basis of research that would be methodologically unacceptable in clinical practice.1 He implies that absolute reductions in accidents can be interpreted in terms of reductions in risk to individuals.
One hypothesis is that traffic calming schemes simply redirect traffic and accidents to other roads, with no overall reduction in risk. The Transport Research Laboratory described the findings of 72 schemes to reduce traffic speeds to ⩽20 mph.2 Information on accidents on surrounding roads was available from only 40 sites, and overall no significant change occurred.
Pilkington accepts the laboratory's conclusion that there was no apparent accident migration on to surrounding roads. But this is absence of evidence that accidents migrate and not evidence of absence. The overall summary statistic masks increases in accidents on surrounding roads of up to 50% in 17 of the 40 sites. Consider basing a clinical decision on these criteria: the harm to benefit odds are only 1:1.4, and the magnitudes of harmful and beneficial effects are similar (21% (range 2-50%) v 24% (3-54%) respectively).
Pilkington drew extensively from a newspaper article that got facts wrong.3 The 30 kph (19 mph) traffic calming measures in Graz, Austria, did not reduce air pollution, and local approval rose to 68% (G Sammer, 76th annual meeting of Transportation Research Board, Washington, DC, January 1997), not “8 out of 10.”1
There is an important distinction between reductions in accidents and reductions in risk, illustrated by the effects of the introduction of laws concerning compulsory use of bicycle safety helmets in Victoria, Australia, in 1990. Deaths and serious injuries in cyclists fell by around a quarter,4 but there was a concomitant reduction of 36% in bicycle use by children. It was not clear whether risk had been reduced or laws had discouraged a healthy activity that should be promoted. Consequently the BMA's board of education and science advised that cycle helmets should not be compulsory in the United Kingdom. Until reductions in accidents after the introduction of traffic calming measures are expressed in terms of risks to pedestrians, cyclists, and motorists we cannot separate numerator and denominator effects.
Evidence for health effects of non-health sector interventions ought to be of the same standard as we require in health services; the potential for health effects is much greater. Would we argue to use a new treatment on the basis of evidence that its potential effects were negligible and its potential side effects included serious injury or death?
References
1.Pilkington P. Reducing the speed limit to 20 mph in urban areas. BMJ. 2000;320:1160. doi: 10.1136/bmj.320.7243.1160. . (29 April.) [DOI] [PMC free article] [PubMed] [Google Scholar]
2.Department of Environment, Transport and the Regions. Review of traffic calming schemes in 20 mph zones. London: DETR; 1996. [Google Scholar]
3.Rogers B. For fewer deaths and less pollution, reduce speed now. Guardian 1999 Aug 18:18.
4.Cameron MH, Vulcan AP, Finch CF, Newstead SV. Mandatory bicycle helmet use following a decade of helmet promotion in Victoria, Australia—an evaluation. Accid Anal Prev. 1994;26:325–337. doi: 10.1016/0001-4575(94)90006-x. [DOI] [PubMed] [Google Scholar]
BMJ. 2001 Jan 6;322(7277):50.
Long term sequelae of road traffic accidents must not be underestimated
Editor—Pilkington highlights the major threat to the lives of children in the United Kingdom that is posed by road traffic accidents.1-1 The devastating consequences for the survivors of these accidents and their families need further elaboration. The chronic sequelae that create difficulties in interpersonal, educational, and social functioning are the behavioural and cognitive problems.1-2 A large proportion of children who sustain a traumatic brain injury after the age of 3 present with emotional problems.1-3 The implications for further education and eventual employment opportunities are obvious.
The acute medical care of individuals with a traumatic brain injury has made considerable advances over the past three decades, resulting in an increased number of survivors. Limited rehabilitation programmes have been developed for these patients in the United Kingdom.1-4 The impact on the individual, the family, and society (including the NHS) is enormous and should not be underestimated. The economic cost (both direct and indirect) of traumatic brain injury is immense.1-5 This takes on added weight when one considers that most people who survive a traumatic brain injury have a normal life expectancy.
Any measure to reduce the incidence of traumatic brain injuries resulting from road traffic accidents should be supported. This includes a reduction in the speed limit to 20 mph (32 kph) in urban areas. As Pilkington points out, other issues such as driver education and enforcement also need to be addressed. The potential for reducing deaths and injuries as well as costs to the NHS may be considerable.
References
1-1.Pilkington P. Reducing the speed limit to 20 mph in urban areas. BMJ. 2000;320:1160. doi: 10.1136/bmj.320.7243.1160. . (29 April.) [DOI] [PMC free article] [PubMed] [Google Scholar]
1-2.Lishman WA. The psychological consequences of cerebral disorder. 3rd ed. Oxford: Blackwell Science; 1998. Organic psychiatry. [Google Scholar]
1-3.Braga LW, da Paz AC. Neuropsychological pediatric rehabilitation. In: Christensen A, Uzzell BP, editors. International handbook of neuropsychological rehabilitation. London: Kluwer Academic; 2000. [Google Scholar]
1-4.Greenwood RJ, McMillan TM. Models of rehabilitation programmes for the brain injured adult. I. Current provision, efficiency and good practice. Clin Rehab. 1993;7:248–255. [Google Scholar]
1-5.Max W, MacKenzie EJ, Rice DP. Head injuries: costs and consequences. J Head Trauma Rehab. 1991;6:76–91. [Google Scholar]
BMJ. 2001 Jan 6;322(7277):50.
Health professionals should ensure that local authorities reduce speed limits
Editor—The positive effect on child health of reducing speed limits in urban areas2-1 should not be underestimated. Road traffic accidents are a major cause of death in children. The silence of organisations such as the Royal College of Paediatrics and Child Health is a great disappointment. If a new drug or vaccine could prevent the deaths of 70 children each year there would be a demand to make it readily available to all communities.
The simple measure of reducing the speed limit in residential areas, near schools and play areas, would not only save lives but also improve the quality of life for residents, especially young and elderly people. Health professionals have a responsibility to ensure that local authorities reduce speed limits, explain why they are doing so, and enforce the new speed limits. If we do not do so then we will continue to kill more children than our European neighbours do.
References
2-1.Pilkington P. Reducing the speed limit to 20 mph in urban areas. BMJ. 2000;320:1160. doi: 10.1136/bmj.320.7243.1160. . (29 April.) [DOI] [PMC free article] [PubMed] [Google Scholar]
BMJ. 2001 Jan 6;322(7277):50.
Both advisory and mandatory speed limits are being introduced in Edinburgh
Editor—Pilkington writes about the benefits of 20 mph (32 kph) speed limits.3-1 Councils throughout Scotland are conducting trials of advisory 20 mph limits as part of a Scottish Executive initiative. In Lothian these are generally in residential areas and often linked with “safe routes to schools” projects. A small number of mandatory 20 mph zones exist, with proposals in Edinburgh for a city-wide 20 mph limit in residential areas and on shopping streets.
Road traffic accidents are not spread evenly across communities; disadvantaged children are much more likely to be involved in them.3-2,3-3 In Edinburgh the city council has made traffic calming measures in areas with high accident rates a feature of its road safety strategy since the early 1990s. These measures have been mainly engineering measures to calm traffic in more disadvantaged parts of the city.
These measures have resulted in lower speeds and a 39% reduction in reported accidents in areas calmed under the casualty reduction programme (versus 29% reduction where environmental traffic management was the aim and 4% reduction where measures were in connection with bus priority routes). This is against a picture of relatively stable accident levels in the council area during the 1990s and suggests that targeting areas with high accident levels can produce good results; it ties in with other Scotland-wide data.3-4
Engineering measures are costly, with the city council spending some £1.2m for the casualty reduction programme. Whether the much less expensive advisory 20 mph schemes will be of similar benefit remains to be seen, but some lessons about implementing and enforcing them have emerged. As the schemes are merely advisory, they can be enforced only if motorists are driving dangerously.
Anecdotal evidence from early schemes suggests that, while speeds are generally falling, many motorists have not moderated their speed. These motorists are often local residents who believe that they know the road (Lothian and Borders Police, personal communication). This emphasises the importance of community consultation before schemes are introduced and regular feedback to the community after they are in place—in Scotland only around a third of residents have rated the consultation as sufficient. Where consultation is good, satisfaction with the scheme put in place is high.
The Scottish needs assessment programme recently conducted a health impact assessment of Edinburgh's transport policy, which endorses the city council's transport policy as a means to promote social inclusion and reduce inequalities.3-5 The policy supports less reliance on cars and promotes walking and cycling, development of public transport, and integrated land use policies.
References
3-1.Pilkington P. Reducing the speed limit to 20 mph in urban areas. BMJ. 2000;320:1160. doi: 10.1136/bmj.320.7243.1160. . (29 April.) [DOI] [PMC free article] [PubMed] [Google Scholar]
3-2.Roberts I. Does the decline in child injury mortality vary by social class? A comparison of class specific mortality in 1981 and 1991. BMJ. 1996;313:784–786. doi: 10.1136/bmj.313.7060.784. [DOI] [PMC free article] [PubMed] [Google Scholar]
3-3.Gorman DR, Ramsay LJ, Bull M, McGuigan D. Uptake of the children's traffic club in Lothian. Health Bulletin. 2000;58:58–62. [PubMed] [Google Scholar]
3-4.Ross Silcock Ltd/Social Research Associates. Community impact of traffic calming schemes. Edinburgh: Scottish Executive Central Research Unit; 1999. . (Development department research programme research findings No 68.) [Google Scholar]
3-5.Scottish Needs Assessment Programme. Health impact assessment of the City of Edinburgh council's urban transport strategy. Glasgow: SNAP; 2000. [Google Scholar]
