Promoting walking and cycling as an alternative to using cars: systematic review
http://www.100md.com
《英国医生杂志》
1 MRC Social and Public Health Sciences Unit, University of Glasgow, Glasgow G12 8RZ, 2 Centre for Digital Library Research, University of Strathclyde, Glasgow G1 1XH
Correspondence to: D Ogilvie d.ogilvie@msoc.mrc.gla.ac.uk
Abstract
Driving cars contributes to traffic congestion, air pollution, and the risk of injury and death to road users, whereas walking and cycling pose little risk to others and provide opportunities for physical activity.1 Increasing physical activity in the population has been described as the "best buy" for improving public health,2 but we have tended to promote physical activity as leisure and through individual behaviour change.3 Could we also achieve this through changes in the transport environment?
Shifting people's approach to transport is now a common objective of transport policies, the overall aims of which may include managing congestion and improving air quality, road safety, and access to services. Various interventions have been advocated or implemented, but evidence of the actual effects of proposed measures is rarely cited, and we cannot assume that apparently sensible measures will be effective or free from harmful effects.4-8 To date, systematic reviews have tended to concentrate on relatively narrow questions about safety.9 We carried out a systematic review of the best available evidence on the effects of population level interventions to promote a shift from using cars towards walking and cycling.
Methods
Principal findings
In this systematic review of interventions to promote a population shift from using cars towards walking and cycling we found evidence from a few relatively well conducted studies that targeted programmes can change the behaviour of motivated subgroups.w1-14 At a population level (in the main TravelSmart study) this resulted in around 5% of all household trips being shifted from cars to walking and cycling. Volunteers participating in trials experienced short term improvements in certain measures of health or fitness after taking up active commuting.w1 w2 w50 w51 Single studies of commuter subsidiesw41 w42 and a new train stationw48 have also shown positive shifts of 1% and 5% of trips, respectively.
The balance of best available evidence about agents of change, publicity campaigns, engineering measures, and charging road users suggests that they have not been effective in our terms.w19-40 w43 w44 We also found evidence from single controlled studies that car share clubsw45-47 and telecommutingw49 were not effective; if anything, participation in these interventions was associated with negative effects.
Strengths and weaknesses of the review
We sought population level evidence to answer a public health question. We therefore searched for a wide range of evidence from diverse sources, making no assumptions about what types of intervention or study design would be relevant, and explicitly considering external validity or transferability (such as the choice of study population) in selecting studies for inclusion.13 We may still have missed some relevant evidence because of poor indexing in some databases. A common objective of synthesising evidence is to pool results and derive generalisable estimates of effect size, but we could not do this because the interventions and studies we found were heterogeneous.
Few systematic reviews of interventions to improve health have explicitly sought evidence of the social distribution of effects. We did seek such evidence but found that it was limited and often not supported by the citation of actual data.
Strengths and weaknesses of the available evidence
In general, the most robust evidence of effectiveness was concentrated around interventions targeted at motivated groups of volunteers. Neither these interventions nor their observed effects are necessarily applicable to larger, less selected populations. Many of the other studies were of poor quality or were poorly reported. We found little evidence of how the effects of the interventions were distributed in the population and no good evidence of how an effective population level intervention had influenced any aspect of population health.
We chose to specify a shift in mode of transport between cars and walking and cycling as our key outcome measure, but relatively few primary studies have reported data about this outcome. Some interventions were not primarily designed to achieve this. Others may have been ineffective in our terms but successful in other terms, such as promoting public transport at the expense of other modes or promoting cycling at the expense of walking. Our difficulty in finding relevant evidence may reflect hitherto different priorities in the transport and health policy and research communities. Walking and cycling have long been marginalised in transport planning, and recognition of their potential wider social benefits remains limited.14 Emerging findings from contemporary interventions such as the London congestion charge or the National Cycle Network suggest that these may be encouraging walking or cycling,15 16 but evaluation studies are often not designed to assess effects on important population health determinants such as physical activity.
Implications and unanswered questions
It is difficult to change longstanding and complex patterns of behaviour so the evidence that some in-depth, targeted interventions have achieved any measurable shift is encouraging. Our findings are consistent with a view that interventions that engage people in a participative process and address factors of personal relevance may be more effective than those that simply aim to raise awareness or impose changes in the physical and economic environments. Some less targeted types of intervention, however, remain to be rigorously evaluated so this view reflects absence of evidence as much as it reflects evidence of absence of effectiveness.17
The authors of two studies stated that observed increases in cycling were largely attributable to existing cyclists making more trips.w3-9 w23-30 Together with the finding that the best evidence of effectiveness is for targeted behaviour change programmes, this raises the possibility that an apparently "successful" intervention could conceal increasing disparities in levels of physical activity between social groups. This requires further research.
Ecological comparisons show that the proportion of walking and cycling journeys can vary between populations, both between and within countries, by an order of magnitude greater than the population effect size of any intervention included in this review.18-21 It may be unrealistic to expect interventions to produce substantial effects in relatively inactive populations without addressing the other, potentially complex reasons for such variations, such as attitudes towards cars and bicycles. Combining interventions in a genuinely integrated urban transport policy might be more effective, but we currently lack evidence from intervention studies to support this assertion.
What is already known on this topic
Transport policies increasingly seek to reduce traffic congestion by discouraging car use and encouraging the use of alternative modes of transport, such as walking and cycling
We lack good evidence either on which interventions are likely to be effective in promoting a shift from using cars towards walking and cycling or on the actual effects of such interventions on population health
What this study adds
Targeted behaviour change programmes can be effective in changing the transport choices of motivated subgroups, but the social distribution of their effects and their effects on the health of local populations are unclear
Evidence that other types of intervention have been effective is inconsistent, of low validity, based on single highly contextual studies, or non-existent
Our findings echo Wanless's more general observation that we know relatively little about the likely impact on health of interventions to influence the wider determinants of population health.22 Many transport policy interventions constitute natural experiments, in which effects on population health could and should be evaluated using well designed prospective (and, where appropriate, controlled) studies. These studies should use varied methods of evaluation to provide multiple perspectives on the supposed causal relation between a complex intervention and its alleged effects. They should assess changes in physical activity and wellbeing, as well as adverse effects such as injuries and the potential for widening social inequalities in health and determinants of health.
Details of the search strategy and study selection, references to primary studies included in the review (w1-w51), five tables of study data, and a flow chart can be found on bmj.com
We are grateful to the numerous colleagues who commented on draft versions of our review protocol and reference list. We also thank David Cumming for advice on literature searching and those who provided clarifications and additional information about studies, particularly Solveig Meland, James Ryle, and Julie Whitehouse.
Contributors: DO and MP had the original idea. DO designed the review with input from MP, carried out study selection, data extraction, and critical appraisal and wrote the paper. All authors contributed to the design of the study and writing of the paper. VH and DO executed the literature search, and ME and MP contributed to study selection, data extraction, and critical appraisal. DO is guarantor for the paper.
Funding: Chief Scientist Office of the Scottish Executive Health Department and the ESRC Evidence Network.
Competing interests: None declared.
Ethical approval: Not required.
References
McCarthy M. Transport and health. In: Marmot M, Wilkinson R, eds. Social determinants of health. Oxford: Oxford University Press, 1999.
Morris J. Exercise in the prevention of coronary heart disease: today's best buy in public health. Med Sci Sports Exercise 1994;26: 807-14.
Dora C. A different route to health: implications of transport policies. BMJ 1999;318: 1686-9.
Department for Transport. A new deal for transport: better for everyone. London: Stationery Office, 1998.
Secretary of State for Scotland. Travel choices for Scotland. The Scottish integrated transport white paper. Edinburgh: Stationery Office, 1998.
Carnall D. Cycling and health promotion. BMJ 2000;320: 888.
Roberts I. Congestion charging and the walking classes. BMJ 2003;326: 345-6.
Petticrew M. Presumed innocent: why we need systematic reviews of social policies. Am J Prev Med 2003;24(3 suppl): 2-3.
Morrison D, Petticrew M, Thomson H. What are the most effective ways of improving population health through transport interventions? Evidence from systematic reviews. J Epidemiol Community Health 2003;57: 327-33.
Clarke M, Oxman A, eds. Cochrane reviewers' handbook 4.1.5. Oxford: Update Software, 2002.
NHS Centre for Reviews and Dissemination. Undertaking systematic reviews of research on effectiveness: CRD report no. 4. York: NHS Centre for Reviews and Dissemination, 2001.
Egan M, Petticrew M, Ogilvie D, Hamilton V. New roads and human health: a systematic review. Am J Public Health 2003;93: 1463-71.
Rychetnik L, Frommer M, Hawe P, Shiell A. Criteria for evaluating evidence on public health interventions. J Epidemiol Community Health 2002;56: 119-27.
House of Commons Health Committee. Obesity: third report of session 2003-04. London: Stationery Office, 2004.
Transport for London. Congestion charging central London. Impacts monitoring: second annual report, April 2004. London: Transport for London, 2004.
Sustrans. The National Cycle Network route user monitoring report to end of 2003. Bristol: Sustrans, 2004.
Alderson P. Absence of evidence is not evidence of absence. BMJ 2004;328: 476-7.
ADONIS Project. Best practice to promote cycling and walking. Copenhagen: Road Directorate, Danish Ministry of Transport, 1998.
Jacobsen P. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Inj Prev 2003;9: 205-9.
Commission for Integrated Transport. European best practice in delivering integrated transport—key findings. London: Commission for Integrated Transport, 2001.
Scottish Executive. Transport across Scotland: some Scottish Household Survey results for parts of Scotland. Edinburgh: Scottish Executive, 2001. (Statistical Bulletin Trn/2001/4.)
Wanless D. Securing good health for the whole population: final report. London: HM Treasury, 2004.(David Ogilvie, MRC fellow)
Correspondence to: D Ogilvie d.ogilvie@msoc.mrc.gla.ac.uk
Abstract
Driving cars contributes to traffic congestion, air pollution, and the risk of injury and death to road users, whereas walking and cycling pose little risk to others and provide opportunities for physical activity.1 Increasing physical activity in the population has been described as the "best buy" for improving public health,2 but we have tended to promote physical activity as leisure and through individual behaviour change.3 Could we also achieve this through changes in the transport environment?
Shifting people's approach to transport is now a common objective of transport policies, the overall aims of which may include managing congestion and improving air quality, road safety, and access to services. Various interventions have been advocated or implemented, but evidence of the actual effects of proposed measures is rarely cited, and we cannot assume that apparently sensible measures will be effective or free from harmful effects.4-8 To date, systematic reviews have tended to concentrate on relatively narrow questions about safety.9 We carried out a systematic review of the best available evidence on the effects of population level interventions to promote a shift from using cars towards walking and cycling.
Methods
Principal findings
In this systematic review of interventions to promote a population shift from using cars towards walking and cycling we found evidence from a few relatively well conducted studies that targeted programmes can change the behaviour of motivated subgroups.w1-14 At a population level (in the main TravelSmart study) this resulted in around 5% of all household trips being shifted from cars to walking and cycling. Volunteers participating in trials experienced short term improvements in certain measures of health or fitness after taking up active commuting.w1 w2 w50 w51 Single studies of commuter subsidiesw41 w42 and a new train stationw48 have also shown positive shifts of 1% and 5% of trips, respectively.
The balance of best available evidence about agents of change, publicity campaigns, engineering measures, and charging road users suggests that they have not been effective in our terms.w19-40 w43 w44 We also found evidence from single controlled studies that car share clubsw45-47 and telecommutingw49 were not effective; if anything, participation in these interventions was associated with negative effects.
Strengths and weaknesses of the review
We sought population level evidence to answer a public health question. We therefore searched for a wide range of evidence from diverse sources, making no assumptions about what types of intervention or study design would be relevant, and explicitly considering external validity or transferability (such as the choice of study population) in selecting studies for inclusion.13 We may still have missed some relevant evidence because of poor indexing in some databases. A common objective of synthesising evidence is to pool results and derive generalisable estimates of effect size, but we could not do this because the interventions and studies we found were heterogeneous.
Few systematic reviews of interventions to improve health have explicitly sought evidence of the social distribution of effects. We did seek such evidence but found that it was limited and often not supported by the citation of actual data.
Strengths and weaknesses of the available evidence
In general, the most robust evidence of effectiveness was concentrated around interventions targeted at motivated groups of volunteers. Neither these interventions nor their observed effects are necessarily applicable to larger, less selected populations. Many of the other studies were of poor quality or were poorly reported. We found little evidence of how the effects of the interventions were distributed in the population and no good evidence of how an effective population level intervention had influenced any aspect of population health.
We chose to specify a shift in mode of transport between cars and walking and cycling as our key outcome measure, but relatively few primary studies have reported data about this outcome. Some interventions were not primarily designed to achieve this. Others may have been ineffective in our terms but successful in other terms, such as promoting public transport at the expense of other modes or promoting cycling at the expense of walking. Our difficulty in finding relevant evidence may reflect hitherto different priorities in the transport and health policy and research communities. Walking and cycling have long been marginalised in transport planning, and recognition of their potential wider social benefits remains limited.14 Emerging findings from contemporary interventions such as the London congestion charge or the National Cycle Network suggest that these may be encouraging walking or cycling,15 16 but evaluation studies are often not designed to assess effects on important population health determinants such as physical activity.
Implications and unanswered questions
It is difficult to change longstanding and complex patterns of behaviour so the evidence that some in-depth, targeted interventions have achieved any measurable shift is encouraging. Our findings are consistent with a view that interventions that engage people in a participative process and address factors of personal relevance may be more effective than those that simply aim to raise awareness or impose changes in the physical and economic environments. Some less targeted types of intervention, however, remain to be rigorously evaluated so this view reflects absence of evidence as much as it reflects evidence of absence of effectiveness.17
The authors of two studies stated that observed increases in cycling were largely attributable to existing cyclists making more trips.w3-9 w23-30 Together with the finding that the best evidence of effectiveness is for targeted behaviour change programmes, this raises the possibility that an apparently "successful" intervention could conceal increasing disparities in levels of physical activity between social groups. This requires further research.
Ecological comparisons show that the proportion of walking and cycling journeys can vary between populations, both between and within countries, by an order of magnitude greater than the population effect size of any intervention included in this review.18-21 It may be unrealistic to expect interventions to produce substantial effects in relatively inactive populations without addressing the other, potentially complex reasons for such variations, such as attitudes towards cars and bicycles. Combining interventions in a genuinely integrated urban transport policy might be more effective, but we currently lack evidence from intervention studies to support this assertion.
What is already known on this topic
Transport policies increasingly seek to reduce traffic congestion by discouraging car use and encouraging the use of alternative modes of transport, such as walking and cycling
We lack good evidence either on which interventions are likely to be effective in promoting a shift from using cars towards walking and cycling or on the actual effects of such interventions on population health
What this study adds
Targeted behaviour change programmes can be effective in changing the transport choices of motivated subgroups, but the social distribution of their effects and their effects on the health of local populations are unclear
Evidence that other types of intervention have been effective is inconsistent, of low validity, based on single highly contextual studies, or non-existent
Our findings echo Wanless's more general observation that we know relatively little about the likely impact on health of interventions to influence the wider determinants of population health.22 Many transport policy interventions constitute natural experiments, in which effects on population health could and should be evaluated using well designed prospective (and, where appropriate, controlled) studies. These studies should use varied methods of evaluation to provide multiple perspectives on the supposed causal relation between a complex intervention and its alleged effects. They should assess changes in physical activity and wellbeing, as well as adverse effects such as injuries and the potential for widening social inequalities in health and determinants of health.
Details of the search strategy and study selection, references to primary studies included in the review (w1-w51), five tables of study data, and a flow chart can be found on bmj.com
We are grateful to the numerous colleagues who commented on draft versions of our review protocol and reference list. We also thank David Cumming for advice on literature searching and those who provided clarifications and additional information about studies, particularly Solveig Meland, James Ryle, and Julie Whitehouse.
Contributors: DO and MP had the original idea. DO designed the review with input from MP, carried out study selection, data extraction, and critical appraisal and wrote the paper. All authors contributed to the design of the study and writing of the paper. VH and DO executed the literature search, and ME and MP contributed to study selection, data extraction, and critical appraisal. DO is guarantor for the paper.
Funding: Chief Scientist Office of the Scottish Executive Health Department and the ESRC Evidence Network.
Competing interests: None declared.
Ethical approval: Not required.
References
McCarthy M. Transport and health. In: Marmot M, Wilkinson R, eds. Social determinants of health. Oxford: Oxford University Press, 1999.
Morris J. Exercise in the prevention of coronary heart disease: today's best buy in public health. Med Sci Sports Exercise 1994;26: 807-14.
Dora C. A different route to health: implications of transport policies. BMJ 1999;318: 1686-9.
Department for Transport. A new deal for transport: better for everyone. London: Stationery Office, 1998.
Secretary of State for Scotland. Travel choices for Scotland. The Scottish integrated transport white paper. Edinburgh: Stationery Office, 1998.
Carnall D. Cycling and health promotion. BMJ 2000;320: 888.
Roberts I. Congestion charging and the walking classes. BMJ 2003;326: 345-6.
Petticrew M. Presumed innocent: why we need systematic reviews of social policies. Am J Prev Med 2003;24(3 suppl): 2-3.
Morrison D, Petticrew M, Thomson H. What are the most effective ways of improving population health through transport interventions? Evidence from systematic reviews. J Epidemiol Community Health 2003;57: 327-33.
Clarke M, Oxman A, eds. Cochrane reviewers' handbook 4.1.5. Oxford: Update Software, 2002.
NHS Centre for Reviews and Dissemination. Undertaking systematic reviews of research on effectiveness: CRD report no. 4. York: NHS Centre for Reviews and Dissemination, 2001.
Egan M, Petticrew M, Ogilvie D, Hamilton V. New roads and human health: a systematic review. Am J Public Health 2003;93: 1463-71.
Rychetnik L, Frommer M, Hawe P, Shiell A. Criteria for evaluating evidence on public health interventions. J Epidemiol Community Health 2002;56: 119-27.
House of Commons Health Committee. Obesity: third report of session 2003-04. London: Stationery Office, 2004.
Transport for London. Congestion charging central London. Impacts monitoring: second annual report, April 2004. London: Transport for London, 2004.
Sustrans. The National Cycle Network route user monitoring report to end of 2003. Bristol: Sustrans, 2004.
Alderson P. Absence of evidence is not evidence of absence. BMJ 2004;328: 476-7.
ADONIS Project. Best practice to promote cycling and walking. Copenhagen: Road Directorate, Danish Ministry of Transport, 1998.
Jacobsen P. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Inj Prev 2003;9: 205-9.
Commission for Integrated Transport. European best practice in delivering integrated transport—key findings. London: Commission for Integrated Transport, 2001.
Scottish Executive. Transport across Scotland: some Scottish Household Survey results for parts of Scotland. Edinburgh: Scottish Executive, 2001. (Statistical Bulletin Trn/2001/4.)
Wanless D. Securing good health for the whole population: final report. London: HM Treasury, 2004.(David Ogilvie, MRC fellow)