Improving health through policies that promote active travel: A review of evidence to support integrated health impact assessment

Abstract

Background

Substantial policy changes to control obesity, limit chronic disease, and reduce air pollution emissions, including greenhouse gasses, have been recommended. Transportation and planning policies that promote active travel by walking and cycling can contribute to these goals, potentially yielding further co-benefits. Little is known, however, about the interconnections among effects of policies considered, including potential unintended consequences.

Objectives and methods

We review available literature regarding health impacts from policies that encourage active travel in the context of developing health impact assessment (HIA) models to help decision-makers propose better solutions for healthy environments. We identify important components of HIA models of modal shifts in active travel in response to transport policies and interventions.

Results and discussion

Policies that increase active travel are likely to generate large individual health benefits through increases in physical activity for active travelers. Smaller, but population-wide benefits could accrue through reductions in air and noise pollution. Depending on conditions of policy implementations, risk tradeoffs are possible for some individuals who shift to active travel and consequently increase inhalation of air pollutants and exposure to traffic injuries. Well-designed policies may enhance health benefits through indirect outcomes such as improved social capital and diet, but these synergies are not sufficiently well understood to allow quantification at this time.

Conclusion

Evaluating impacts of active travel policies is highly complex; however, many associations can be quantified. Identifying health-maximizing policies and conditions requires integrated HIAs.

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).