ReviewImproving health through policies that promote active travel: A review of evidence to support integrated health impact assessment
Research highlights
► Active travel policies are growing in popularity worldwide. ► We review multiple benefits and potential risks associated with policies. ► Quantitative relationships for health impact assessments are discussed. ► Major health benefits are especially expected from physical activity outcomes. ► Well designed policies may enhance co-benefits and mitigate risks.
Introduction
The past decade has seen an enthusiasm for planning cities for health, which had mostly been forgotten since the urban sanitarian movement in the mid-nineteenth century (Corburn, 2007). Triggers for this renewed interest include concerns about obesity, physical inactivity, pollution, climate change, and road traffic injuries. Physical inactivity is one of the most important health challenges of the 21st century because of its influence on the most deadly chronic diseases, contributing worldwide to 21.5% of ischemic heart disease, 11% of ischemic stroke, 14% of diabetes, 16% of colon cancer and 10% of breast cancer (Bull et al., 2004). The World Health Organization (WHO) recently estimated overweight and obesity to be responsible for 2.8 million deaths annually; physical inactivity is (separately) responsible for an additional 3.2 million deaths (WHO, 2009). The apparent limitations of classic individual-based physical activity (PA) and dietary interventions have raised the interest of health professionals in community-level solutions that encourage healthy behaviors in daily routines (Lavizzo-Mourey and McGinnis, 2003).
Disease and mortality associated with vehicle emissions also represent a substantial challenge in public health. Urban air pollution currently accounts for instance for ~ 3% of mortality from cardiopulmonary disease, and 1% of mortality from acute respiratory infections in children under 5 years, worldwide (Cohen et al., 2005). These figures may worsen as the proportion of the population living in cities continues to rise (currently 50%, projected to reach 70% in 2050) (U.N., 2010). Vehicle emissions also contribute to climate change, recognized as a widespread threat to human health (Haines et al., 2009). The share of transport activities in GHG emissions (23% worldwide) continues to grow at a faster rate than any other end-use sector and the reduction of on-road emissions has been identified as the most effective strategy to reduce radiative forcing (Unger et al., 2010). The magnitude of reductions in emissions required to slow the buildup of greenhouse gases (GHG) is such that multiple solutions are needed, including changes in travel behavior (Boies et al., 2009). Another health impact of vehicle usage is traffic injuries, which is the second leading cause of death for people age 5–29 (WHO, 2004b). The rapid increase of auto sales and use is thus likely to have important impacts on public health (HEI, 2010).
International groups including the World Health Organization (WHO), the United Nations (UN), and the Intergovernmental Panel on Climate Change (IPCC) have recommended policy changes to combat physical inactivity, pollution, climate change, and traffic injuries (IPCC, 2007, U.N., 2010, WHO, 2004a). Transportation and planning policies promoting walking and cycling as alternatives to using private motor vehicles can contribute to these goals, with the potential for gaining further co-benefits such as congestion mitigation. At the same time, concerns have been raised about the potential to increase the risks of injuries and exposure to air pollution for pedestrians and cyclists (de Hartog et al., 2010, de Nazelle et al., 2009, WHO, 2006, Woodcock et al., 2009). Changes in how we design and build cities are important, but little is known about the interconnections among the changes and policies being considered. Fortunately, awareness of this topic is increasing (Dannenberg et al., 2006).
Major connections among transportation policies, planning, and health are summarized in Fig. 1, and reviewed in the next sections. Further important indirect health and other co-benefits of policies that encourage active travel are not specifically addressed here but have been reviewed elsewhere. These include improved mobility (in particular, access to healthcare services), curtailed social inequalities, and reduced congestion and road and parking costs (Litman, 2008). Generally, congestion and vehicle emissions are the primary indicators considered in evaluations of planning and transportation decisions.
Additional evidence, tools and methods are needed to evaluate transportation policies and the full range of their health impacts. In this context we review current knowledge of how health is affected by active travel and associated policies or contextual factors. Our purpose is to develop a framework for conducting integrated health impact assessments (HIA, Briggs, 2008, Dannenberg et al., 2006) useful for decision makers to develop optimal policies for health-promoting environments. We identify important components of an HIA, assess the existence and applicability of exposure–response functions (ERFs) and environmental models available to quantify relationships linking active travel-related policies to environmental indicators and to health impacts, and discuss how various exposures and outcomes interact with each other. This article is not a systematic review but rather an evaluation of the pertinence and possibility of quantifying potentially relevant impacts. Our goal is to make a case for formally conducting such assessment to better inform policy decisions for healthier urban environments.
We first propose a conceptual framework to assess health effects of policies that promote active travel. The framework guides our literature review of the most relevant fields of behavior, environmental quality and health. We cover relationships for which the research is most extensive and the evidence strongest as well as the quantitatively less well-established links between active travel policies and health or health determinants. We limit our discussion to adults as they are the decision-makers for most travel choices, even though children are also affected in important ways by active travel policies (or lack thereof) (Marshall et al., 2010, Wilson et al., 2010).
Section snippets
Conceptualization of transport policy impacts on health
The empirical evidence linking characteristics of city and regional land use and transport planning directly with health outcomes has mostly emerged in the past ten years. Pioneering studies showed that people living in areas of urban sprawl (dispersed low-density single use land patterns) were more likely to be overweight or obese (Ewing et al., 2003b, Lopez, 2004), suffer more from hypertension and other chronic diseases (Ewing et al., 2003b), and experience greater traffic fatalities,
Active transportation policies and interventions
A growing body of literature suggests likely positive impacts of travel policies and interventions to increase walking and cycling (Pucher et al., 2010). The little research providing direct evidence based on rigorous longitudinal assessment designs shows moderate, albeit consistent, effectiveness of such interventions in changing behaviors (Ogilvie et al., 2007, Yang et al., 2010). Bundles of strategies are often implemented together, ranging from promotional campaigns to changes in the
Environmental quality
Large-scale travel mode conversions from conventional-vehicle trips to active travel will reduce vehicle emissions, greenhouse gases, noise, and perhaps urban heat island effects. We first review traffic emissions and environmental quality, and in Section 4.2 discuss implications for exposures in the population. Health impacts are covered in Section 5.
Health benefits of PA and active commuting
A substantial body of research has provided compelling evidence of associations between regular PA and various health outcomes in adults. Health agencies generally recommend 30 min or more of moderate-intensity PA on most days of the week for good health (Haskell et al., 2007, US DHHS, 2008). These recommendations correspond to weekly energy expenditures of ~ 8 MET-hr, or 750 kcal, over basal levels, and are associated with ~ 30% reductions in all-cause mortality, cardiovascular disease and type 2
Discussion
We reviewed evidence for the relationships between active travel and components of active travel policies and health, indicating potential synergistic, feedback or competing effects of different components of policies, and highlighting relationships for which knowledge is strongest or weakest for integration in a quantitative HIA (Fig. 1: variables in bold are those identified having the most robust exposure-health quantifications available, while those in italics are those for which the least
Conclusion
Policy decision-making, whether concerning the environment, health, or urban planning, has often been criticized for being piecemeal and selective (Duany, 2002). With the growing interest in active travel as a solution to physical inactivity, urban air pollution, and climate change, it is important to recognize the complexity of interactions among people, places, and the natural environment. This review contributes to making the case for more integrative approaches to decision-making, in
Acknowledgments
Contributions from the various authors were discussed and developed during a workshop held on November 9–10th 2009 for the launch of the Transportation Air pollution and Physical ActivitieS: an integrated health risk assessment program of climate change and urban policies (TAPAS) project. TAPAS is a four year project funded in part by the Coca-Cola Foundation and the Agencia de Gestio d'Ajuts Universitaris i de Recerca. The funders have no role in the planning of study design; in the
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