Medicine & Science in Sports & Exercise:
Correlates and Intervention of Walking Behavior
Built Environment Correlates of Walking: A Review
SAELENS, BRIAN E.1; HANDY, SUSAN L.2
1Department of Pediatrics, University of Washington and Children's Hospital and Regional Medical Center, Seattle, WA; and 2Department of Environmental Science and Policy and Institute of Transportation Studies, University of California, Davis, CA
Address for correspondence: Brian E. Saelens, Ph.D., University of Washington Child Health Institute, 6200 NE 74th St, Suite 210, Seattle, WA 98115; E-mail: email@example.com.
Introduction: The past decade has seen a dramatic increase in empirical investigation into the relations between built environment and physical activity. To create places that facilitate and encourage walking, practitioners need an understanding of the specific characteristics of the built environment that correlate most strongly with walking. This article reviews evidence on the built environment correlates with walking.
Method: Included in this review were 13 reviews published between 2002 and 2006 and 29 original studies published in 2005 and up through May 2006. Results were summarized based on specific characteristics of the built environment and transportation walking versus recreational walking.
Results: Previous reviews and newer studies document consistent positive relations between walking for transportation and density, distance to nonresidential destinations, and land use mix; findings for route/network connectivity, parks and open space, and personal safety are more equivocal. Results regarding recreational walking were less clear.
Conclusions: More recent evidence supports the conclusions of prior reviews, and new studies address some of the limitations of earlier studies. Although prospective studies are needed, evidence on correlates appears sufficient to support policy changes.
Walking is one of the most common forms of physical activity, with documented benefits for health (36,48). Research on walking behavior has traditionally focused on individual factors such as socio-demographic characteristics and attitudes (59). Intervention studies have usually addressed the individual or social environment, through incentives, individually targeted behavior change programs, worksite programs, and walking clubs and other activities designed to increase social support for walking (38) although some have targeted more changes in environment (e.g., building/extending walking paths) (53). Researchers and practitioners alike have come to appreciate the importance of the built environment in facilitating or constraining walking. Walking occurs primarily in neighborhood streets and public facilities (44), and the character of such places influences the degree to which they are safe, comfortable, and attractive for walking. To create places that facilitate and encourage walking, practitioners need an understanding of the specific characteristics of the built environment that correlate most strongly with walking.
The built environment has been defined in different ways by different researchers. Most generally, it is defined as the part of the physical environment that is constructed by human activity. By one definition, the built environment consists of the following elements: land use patterns, the distribution across space of activities and the buildings that house them; the transportation system, the physical infrastructure of roads, sidewalk, bike paths, etc., as well as the service this system provides; and urban design, the arrangement and appearance of the physical elements in a community (32). Researchers have also focused on different types of walking, whether walking for recreation or exercise or walking to reach a destination. This latter category has a variety of labels, including active travel, nonmotorized travel, transport-related physical activity, destination-oriented walking, and utilitarian walking. Bicycling and transit use, which usually involves walking and sometimes involves bicycling, are often included with walking under the first three labels, though walking is generally the largest component.
Research on the built environment correlates of walking has proliferated in recent years. Two different fields have contributed to this body of work. The transportation planning field has for several decades studied the connection between the built environment and travel behavior. Although the motivation for this work has been a concern over the growing amount of automobile traffic, researchers have also considered the effect of the built environment on walking as a mode of transportation (32,58). The public health field has long studied walking as a form of physical activity but in the last decade has increasingly focused on the connection between the built environment and walking for recreation or exercise or walking in total (37,44,54). In the last several years, researchers from these two fields have worked together to better understand these connections. This article reviews what the research so far tells us about the characteristics of the built environment that correlate with walking and discusses outstanding questions and policy implications.
Many reviews of the research on built environment correlates of walking have been published. A review of these reviews is provided before examining more recent studies. To identify all relevant reviews, reviews already known (and some written) by the authors were examined and searches were conducted in the Pub Med, TRIS, and Academic ASAP databases using the terms "walk," "walking," "pedestrian," "nonmotorized," and "active travel" for reviews. After screening obtained reviews for relevance, we considered nine reviews published between 2002 and 2006 (2,18,33,37,44,49,52,54,58), three additional articles that discuss research issues but do not systematically review results (27,32,47), and one extensive review published as appendix to an Institute of Medicine-Transportation Research Board report (29). Conclusions based on studies reviewed, limitations of those studies, and recommendations made for future studies were extracted from these review articles.
Previous reviews provide important insights into specific characteristics of the built environment correlated with walking behavior and into the limitations of this research. Only two of the reviews we identified focus on walking specifically (54,58), while the other reviews include studies of physical activity more generally but distinguish results for walking. Although there is considerable overlap in the studies included in the different reviews, each review used somewhat different criteria and search procedures for identifying relevant studies. As several of these reviews note, differences across studies in measures of walking and characteristics of the built environment as well as study design make comparisons and conclusions difficult (2,3,58). Still, these reviews provide tentative conclusions that are largely consistent with one another, as summarized in Table 1.
A systematic search was conducted to identify articles published in 2005 and up to May 2006 that examined the link between built environment and walking. Search terms used in PubMed, TRIS, and Expanded Academic ASAP limited to articles published in 2005 or 2006 included "walk," "walking," "environment," "urban form," "pedestrian," "design," and "neighborhood". The bibliographies compiled by the Robert Wood Johnson Foundation Active Living Research Program were also searched. In addition, the Journal of Physical Activity and Health and the Journal of the American Planning Association were searched given their recent supplement issues on physical activity and built environment. The bibliographies of all articles derived from these searches were examined to identify any other pertinent articles.
The articles met the following inclusion criteria: (1) examined some aspect of the physical environment, either objective or perceived, up to and including the broad distinction of urban versus rural; (2) measured walking or walking and cycling as a distinct type of transport and/or activity (e.g., not included within another specific type of physical activity (64) or when grouped among all physical activity); and (3) written in English. Physical environment was operationalized as the built or natural environment, but also included constructs examined in transportation and urban planning literatures as potentially relevant to nonmotorized transport, including population density. In addition, potential derivatives from the physical environment, including aesthetics and safety are also considered. To more specifically focus on physical environment, intrapersonal and interpersonal/social, cultural, and economic environmental factors were not examined (and not included as results), although many studies of physical environment reviewed included such factors.
Table 2 details the sample, environmental data source, environmental factor(s) examined, the analyzed geographic unit of environmental factor(s), walking metric, nonenvironmental covariates examined, and a summary of results of studies conducted among adult samples that examined relations between physical environment and walking. For the environmental data source, "survey" or "interview" denotes that sample respondents were queried about their perceptions or awareness of environmental factors near their residence or in their neighborhood (see geographic unit column for specific area). Under environmental factor(s) examined, objective environmental data were considered data derived from nonrespondent sources including Census, land use, network, and professional or trained raters. In contrast, perceived environment data were considered data about the environment derived from respondents who were also providing information about their walking. When specified, the geographic unit for the objective environment data is provided in Table 2, with the geographic unit for most perceived environment factors being vague in many studies (e.g., respondents asked to describe their "neighborhood"). In Table 2, environmental factors examined are succinctly described, but for brevity reasons, other variables that were also considered and/or are statistically significant correlates (e.g., demographics, psychosocial variables) are not detailed in Table 2. However, the types of covariates, if any, used in the multivariate models in these studies are provided in Table 2. Demographic covariates ("Demos") include such factors as individual respondent age, race/ethnicity, and education level, as well as household level factors including car ownership and household income information; psychosocial-physical activity covariates ("Psych-PA") include individuals' cognitions and other perceived support or barriers to walking or physical activity (e.g., self-efficacy, enjoyment, social support); self-select covariates ("self-select") include individuals' preferences for or attitudes about neighborhood or transport characteristics (e.g., reasons for moving to neighborhood, preference for being able to walk to stores, pro-transit attitudes). All studies presented in Table 2 relied on participant report (usually through surveys) of walking behavior; none used a more objective assessment of walking. Results are presented for findings for each walking outcome available that is statistically significant as described by the study authors (usually P < 0.05, but at times P < 0.10). When multiple models are provided in the article (e.g., base models with a limited number of variables), the final or most complete model results are presented.
Table 3 is an extracted summary of the studies detailed in Table 2, with information for each study on how the environment was measured (through objective means or respondent perceptions), categorizing the scale of the environmental measures and type of walking examined, and summarizing the results into whether the association(s) between the environmental factors were expected, null, or unexpected. Expectedness was based on prior empirical literature and active living conceptual models in the areas of built environment, physical activity, and walking. "Greater or better" of the following built environment constructs were "expected" to be related to more or more frequent walking: density, proximity to nonresidential, street connectivity, parks/open space, pedestrian infrastructure, aesthetics, and nonpark physical activity facilities. In contrast, "less or lower" of the following built environment constructs were "expected" to be related to more or more frequent walking: distance to specific nonresidential land uses, crime, traffic safety, or volume/noise. For simplicity sake and based on the relative lack of empirical evidence regarding specificity of built environment factors for recreational walking, "expectedness" was considered the same for transport, recreation, and general walking outcomes. If an environmental factor was reported as being measured, but not discussed in the article as either significant or nonsignificant, the association between that environmental factor and the walking outcome was categorized as "null." "Urban" versus "rural" comparisons were assigned to the environmental factor of density (based on the Census distinction), although these types of areas also differ on many other environmental factors.
Table 4 is a further extracted summary, grouping each result provided in Table 3 into specific environmental factor types by walking type and result expectedness (expected versus null or unexpected). Thus, it is possible for any given study or sample to provide more than one result (e.g., if a study looked at more than one type of walking, or if a study found some environmental factors related to walking but others not related to walking). For results with composite environmental measures (e.g., Ref. 23), each environmental factor type within the composite was assigned a result in Table 4.
Table 5 details studies looking at physical environmental factors related to children's walking, with most studies examining walking to school. The format of Table 5 mimics that of Table 1, with information provided about sample, environmental data source, environmental factor(s) examined, the geographic unit of the environmental factor measured, the walking metric, and results of each study. Similar to the studies among adults, children's walking behavior was usually assessed by self-report or parent-report, with one exception where walking behavior to school was observed at the beginning of the school day (60).
Review of prior reviews.
The most consistent set of conclusions relates to proximity to potential destinations. Five reviews found sufficient evidence to conclude that accessibility based on distance to destinations is associated with more walking (Table 1). Three reviews concluded that mixed land use is also associated with more walking. Because mixed land use means destinations are within closer proximity, this finding is consistent with the findings for accessibility. Three reviews point to density as an important correlate of walking. This finding is also probably related to proximity: in areas with higher density, destinations can be closer together because the number of people needed to support any activity is found within a smaller area. However, both mixed land use and density might also influence the esthetic qualities of the walking environment and thus as correlates of walking would reflect the combined effect of proximity and aesthetics.
Indeed, six reviews found sufficient evidence to conclude that esthetic qualities-the attractiveness of the environment-are associated with walking. However, measures of this attribute of the built environment are especially variable across studies. Sidewalks (pedestrian infrastructure) and the connectivity of routes/network, attributes of the built environment related to the transportation system, were also found to be correlated with walking. The role of sidewalks in creating safe environments for walking is obvious, while street connectivity is important because of its effect on proximity, greater street connectivity generally means more direct routes and thus shorter distances from home to potential destinations. Street connectivity might also affect walking by expanding the choice of routes, thereby enabling some variety in routes within the neighborhood or to destinations. Attributes related to safety were found by four reviews to be correlates of walking. Finally, three reviews concluded that neighborhood type, defined by "walkability" (generally composite of the above attributes) or by age of development, is a correlate of walking.
The reviews are consistent in their conclusion that the built environment is associated with walking, though they are also consistent in noting that the specifics of this association are less clear. Evidence suggests, for example, that different attributes of the built environment are associated with walking for exercise than with walking as a mode of transportation (29,54). One review found that only one out of four studies showed significant associations between built environment attributes and utilitarian walking (54), while another concluded that utilitarian walking accounts for most of the difference in walking between neighborhoods that differed on built environment characteristics (58). As of the writing of these reviews, the number of available studies was insufficient to produce "definitive conclusions" on the relationship of particular attributes of the built environment with particular walking behaviors (54,58).
The reviews also point to many limitations of this research and provide recommendations for future studies with respect to conceptual models, the specificity of behaviors and environments, measures of the built environment, measures of walking, sampling, focus on specific populations, research design, and collaborations. Many reviews point to the need for better conceptual models to guide future studies (2,29,32,37,54,58). Most generally, researchers need to look at "structural relationships between variables" and undertake a "deeper examination of direct and indirect relationships, interactions, and hypothesized paths of causality" (52). Researchers must give further consideration to confounding factors, which have been inconsistently evaluated in previous studies (44,58). Multilevel models that take into account moderators and mediators should be used, and theoretical models "that account for environmental influences and their interactions with other determinants" are needed (54). Examining the interaction between psychosocial and environmental variables (29,54,58), as well as the interaction between social and physical environments (33) may also be important. Others call for behavior-specific and environment-specific models (27,54). Reviews by researchers from the planning field recommend that planners make use of the social ecological model widely used in health behavior research (29,44).
Another common recommendation is to study specific behaviors in specific environments (27,29,37,49,54). Such an approach will "help identify the particular environmental attributes that might prompt and maintain habitual physical activities" (54). One of the challenges in a carrying out a behavior-specific approach is to properly define neighborhoods in terms of boundaries and scales (27). At issue is the scale at which the neighborhood environment is most strongly correlated with walking and other physical activity (33). In these studies, data on walking must be spatially matched with data on the built environment (32).
Validated, consistent, and objective measures of specific features of the built environment are essential for this work (18). Many reviews call for the use of objective measures generated with the help of geographic information systems (GIS) (18,33,49,54,58). Others suggest that both perceived and objective measures should be included, and researchers should examine the relationship between them, particularly for characteristics such as safety (18,33,49,58). One review calls for a better conceptualization of the built environment to guide the measurement of its components (33), and another review offers one: the Behavioral Model of Environment categorizes characteristics as relating to origin-destination, route, or area (44). The measurement of the quality of built environment elements, not just their presence, is another recommendation (27). Specific characteristics of the built environment identified as in need of better measurement include: personal safety as differentiated from traffic safety (49); walking infrastructure such sidewalks, pedestrian signals and islands, bicycle lanes and trails (58); and traffic-calming measures (2).
Although less of a problem, improved measures of walking are also needed, particularly separate measures for different types of walking (29,44,54). Optimal methods for collecting self-reported data on walking by type, i.e., for recreation versus for transportation, have not yet been established (33). In the planning field, data on walking for transportation are incomplete (32) and the measures are not usually validated (44). In addition, separating walking for recreation from walking for transportation is not necessarily straightforward (29).
Sampling has also been identified as a problem in the reviews. As of the writing of these reviews, studies had been conducted in only a small number of cities (58) and were country-specific (2). Future studies, one review suggests, should select subject samples from heterogeneous environments rather than selecting random samples from general population to ensure sufficient variation in measures of the built environment (27). Another review discusses the problem of spatial multicollinearity of neighborhood characteristics, which makes it hard to identify the unique contribution of specific characteristics; to solve this problem, researchers should compare neighborhoods that differ on only one walkability factor (58).
Few studies have focused on specific segments of the population, leaving open the question of whether the built environment has similar effects by race/ethnicity, socio-economic status, age, or ability (33). Very little research has been done on the relationship between the built environment and children's walking (52). This situation is much the same for older populations, for whom "surprisingly little is known" about the effect of the built environment on walking (18). Further investigation to understand perceived and real barriers for different populations, especially groups with low SES and limited auto access, is needed (2).
As each of these reviews notes, almost all previous studies have been cross-sectional. Cross-sectional studies need to be complemented by and lead to prospective studies to more definitively establish causal relationships between the built environment and walking (2,27,29,33,37,44,49). Research designs that could prove useful in exploring causal relationships include intervention studies that examine change in behavior before and after a change in the built environment (29,53,58), and studies that examine changes in behavior before and after a move from one environment to another (29,58).
Finally, several reviews point to a need for collaborations among a wider range of professionals (2,32,58). It is clear from our review of more recent research that such collaborations are increasing in number and paying off in terms of an improved understanding of the relationship between the built environment and walking.
Evidence from recent research.
For the 2005 and up to May 2006 publication years, we found 29 studies examining 28 different adult samples that examined the relation between built or physical environment factors and walking (Table 2). These studies were drawn from samples across the US, Australia, Portugal, Belgium, and the Netherlands. Almost half the studies included an environmental measurement based solely on objective information, a significant improvement over prior research. There was considerable variability in the type of walking assessed, ranging from walking to a specific location (5), to a specific type of walking such recreational walking (21) or walking to a store (30) to total (26) or general walking (e.g., walking activity 46). Although most studies obtained a continuous assessment of frequency or duration from participants, it was common to evaluate categorical outcomes of walking (7). It is noteworthy that demographic variables were a common type of covariate included in the existing multivariate analyses, with most studies examining individual-level demographic factors rather than both individual- and neighborhood-level demographic characteristics (see Ref. 26 as an example of an exception).
As evidenced in Table 3, most studies have investigated environmental factors at the microlevel, using an individual's residential location and walking distance radius around that location as the environmental scale. As encouraged by others (27), there is more focus on matching specific environmental factors to specific types of walking (transport-related or recreational) and more studies than in the past that have evaluated separately transport and recreational walking.
Studies published in 2005 and the first part of 2006 document consistent positive relations between walking for transportation and density, distance to nonresidential destinations, and land use mix (see Table 4). For transportation walking, findings for route/network connectivity, parks and open space, and personal safety are more equivocal with approximately equal numbers of expected versus null/unexpected results. In contrast, there was little or no evidence in these studies for relations between transportation walking and pedestrian infrastructure conditions, traffic-related issues, aesthetics, or accessibility of physical activity facilities.
Results for the 2005-2006 studies regarding recreational walking were less clear, in part due to the fewer number of such results. In contrast to transportation walking, pedestrian infrastructure and aesthetics evidenced associations with recreation walking, as did personal safety and land use mix, although these latter two factors also had similar number of expected and null/unexpected results. There was little or no evidence among these studies for associations between recreational walking and density, distance to nonresidential destinations, route/network connectivity, parks and open space, traffic, and accessibility of physical activity facilities.
For most of the environmental factors, findings for general or total walking were balanced between expected versus null/unexpected. There were two more expected than null/unexpected findings for route/network connectivity and traffic, but little evidence that general or total walking was related to distance to nonresidential destinations.
The evidence for environmental factors related to children's walking is considerably more scant than for adults, and with the exception of one study (13), focus on the trip to/from school. Although not universally found (13,60), walking to school appears consistently positively related to closer proximity to school, greater population density, and good pedestrian infrastructure and traffic safety on the walk to school route. Indeed, sidewalk and traffic safety improvements along the route increased walking to school rates (6). Findings regarding walking to school and either personal/crime safety or land use mix were more equivocal.
Empirical investigation into associations between walking and built environment factors has expanded considerably during the past few years. Indeed, based on prior reviews of this literature, the number of publications in 2005 to early 2006 on this topic appears to have exceeded any other prior period. Many of the conclusions from prior reviews are supported by this more recent evidence, particularly in the consistent associations found between walking for transportation purposes and density, land use mix, and proximity of nonresidential destinations. More recent evidence also suggests that these factors are not necessarily related to recreation walking or to total amount or frequency of walking, providing some confirmation of this conclusion of some prior reviews. In contrast to some prior work, recent evidence less consistently found a relation between transportation walking and pedestrian infrastructure, such as sidewalk presence and condition, although pedestrian infrastructure was more consistently related to recreation walking.
In addition to recent evidence bearing upon prior results, the past few years have seen considerable progress toward addressing some limitations raised in prior reviews. One advancement has been the greater use of more objective measures of physical or built environment when examining correlates of walking. This is particularly evident with objective measures at the microlevel scale, which is objectively operationalizing the built environment around an individual respondent's residence (23,42,43,46) rather than at a larger scale (e.g., Census tract, city) that may or may not be completely applicable to a given individual. Whereas many studies purposefully include whole neighborhoods or communities that are most uniform within and in contrast to others (14), objective measures at the micro-scale also allow for simultaneous evaluation and direct comparisons to perceptions of the built environment around one's residence. However, these comparisons are made challenging by the different strategies used to evaluate perceived environmental factors and the lack of information about how individuals define their neighborhood. For example, when queried about their neighborhood, it is not clear whether individual respondents are considering a specific radial distance from their home in all directions with influence diminishing with greater distance or an area surrounding their home having an equal amount of influence across that area. In the former case, measures differ from household to household, depending on their location within the neighborhood, and are called micro-level measures; in the latter case, every household within the neighborhood is assumed to experience the same built environment characteristics, and measures are labeled mesolevel. Other advancements include the greater diversity in environmental factors studied from the street level to the neighborhood level and even regional level, more specificity in measurement for environmental factors and walking, the inclusion of more age-diverse samples and examination of demographic variables as moderators (e.g., gender; ), although middle-aged adults are still predominantly studied.
The evidence regarding children is primarily restricted to factors related to walking to school, for which proximity, density, and the quality of the pedestrian infrastructure and traffic safety appear to play roles. Proximity and density findings for active commuting to/from school are among the potent correlates among adults' transportation walking, but the latter factors of pedestrian infrastructure and traffic safety may be more important for children for this type of walking trip. In addition to the limited types of walking outcomes (e.g., walking to school only rather than walking for other purposes or overall), the studies involving children were less likely to consider potential confounding factors, such as demographic or psychosocial variables related to physical activity. To our knowledge, no child-sample studies have examined whether self-selection factors are potentially confounding environment-walking associations in children, perhaps because such factors could be considered more under caregiver control.
The issue on which researchers have made the least progress in examining relations between environment and walking is causality. Prospective designs, a better approach for establishing causality than cross-sectional designs, are costly and complex. Until such studies are completed and replicated, it is not possible to say with certainty that changes in the built environment will lead to increases in walking. Still, by identifying environmental correlates of walking, cross-sectional studies offer guidance as to how to increase opportunities for walking. Further, the measurement and control for potential confounding factors in the relation between built environment and walking, including demographic and self-selection factors (11), lends more credence to a true causal relationship. It was common in recent studies to include demographic covariates (e.g., age, gender, income/education level), with some variability in the specific demographic factors considered across studies, but less common to include psychosocial correlates of physical activity and self-selection as potential confounders. More uncommon, although likely warranted, is the need to evaluate and analyze demographic and other potential confounding variables at both the individual respondent and larger environment level (e.g., neighborhood). This is particularly important given the multilevel nature of the data and the need for corresponding multilevel analyses (9), with such type of analyses not universal in the studies reviewed.
Cross-sectional studies of the built environment and walking have been most loudly criticized on the issue of self-selection, observed associations between the built environment and walking are potentially explained by the prior self-selection of residents into a built environment that is consistent with their predispositions toward walking. The limited evidence available suggests that self-selection occurs but that the built environment influences walking even after accounting for self-selection (30). Several different methods short of prospective design have been used to control for self-selection in the transportation planning field; these studies also point to an impact of the built environment after controlling for self-selection, though the magnitude of the effect varies across studies (12). These methodologies might profitably be applied to future studies of walking.
Studies on the built environment and walking have also been criticized on the grounds that they do not account for the possibility that walking, particularly transportation walking, substitutes for other forms of physical activity. There is however little empirical evidence examining substitution between transportation-related and recreational walking, with the exception of a few studies among youth samples that found that children who walked to school were more physically active than their nonactive commuting peers (no evidence of substitution; [1,17]). This issue can in part be addressed by better matching of behaviors such as walking with the specific environments in which the behavior occurs. As noted earlier, several reviews stress the importance of matching specific measures of the built environment to specific types of physical activity (27). For example, neighborhood built environment should be most closely linked to physical activity that occurs outdoors within the neighborhood. From a conceptual standpoint, the connection between neighborhood built environment and overall physical activity should be rather tenuous, as physical activity occurs in many settings other than the neighborhood. Nevertheless, it is important to understand how different types of walking contribute to overall physical activity. It is possible that an increase in transportation walking resulting from a change to the built environment substitutes for other forms of physical activity without increasing overall physical activity, but empirical evidence regarding this potential substitution is generally lacking.
There are limitations to the present review of reviews and evaluation of recent evidence. First, some of the prior reviews were representative reviews and not meant to be comprehensive of all available prior evidence. Further, to our knowledge, there exists no rigorous quantitative review (e.g., meta-analysis) of this evidence, perhaps in part due to the multitude of environment factors examined, differences in operationalizing of these factors, differences in analysis structures (e.g., multilevel versus not multilevel; examining independent effects of a given environmental variable in the context of others or as a composite) and different methods for measuring walking. Such issues and inconsistency in data/analysis reporting preclude even the more recent evidence from being reviewed systematically and make a meaningful assessment of effect sizes impossible. The lack of more complete conceptual models for recreational walking distinct from transportation walking also makes ambiguous the assignment of result expectedness in the present review of recent empirical articles. For example, a positive relation between recreation walking and density was "expected," but theoretically, it is not surprising that recreational walking is not positively or at all related to density.
Other researchers who have reviewed the evidence have concluded that it is sufficient as a basis for advocating for changes in planning policies. For example, one review concludes that a "preponderance of evidence" suggests that community-scale urban design and land use policies and practices "can be effective in increasing walking and bicycling" and that mixed land use and sidewalk quality and connectivity are "helpful practices," as are improved lighting and enhanced aesthetics at the street scale (33). Another review offers these lessons for practice: evidence points to latent demand for walking suggesting an opportunity to increase walking through improved environments; needed improvements include increased land use intensity and mix along with investments in walking infrastructure; and planners should focus efforts on enablers and constraints on walking (44). The review of prior reviews and recent empirical evidence regarding built environment factors and walking support such recommendations. The available evidence backs the efforts of cities throughout the United States to increase the viability of walking through innovative planning policies. These policies shape both land use patterns and the transportation system and influence aesthetic qualities as well (31):
* Land Use Patterns: many cities have designated mixed-use zoning districts, in which residential, commercial, and other uses are allowed or even required. In these areas, residents are near places to work, shop, and recreate, and the potential for walking is greater. Infill development and redevelopment programs provide incentives for developers to use parcels within an existing urban area and can help with the adaptation of older buildings for new uses. Designation of selected areas as historic districts helps to protect the neighborhood character. In suburban areas, older strip malls have been rebuilt as mixed-use projects, with retail, office, and residential on one site, an approach called "grayfield" redevelopment. Each of these programs aims to retain or attract work, shopping, and leisure activities in or near residential areas and foster attractive and interesting environments, thereby supporting walking.
* Transportation System: traffic-calming programs, common in cities throughout the US, attempt to slow down or discourage automobile traffic and thus make streets safer and more attractive for pedestrians and others. Traffic-calming techniques emphasize the physical design of streets and their surroundings, including widening sidewalks, narrowing the width of streets at pedestrian crossings, adding landscaping, adding measures to slow vehicles such as speed bumps, altering road alignments, adding traffic circles, or installing pavement treatments. In addition, a growing number of cities have adopted ordinances designed to increase street connectivity. Although the primary aim of these ordinances is to spread vehicle traffic more evenly through the network, they also make routes from one point to another more direct, making walking more feasible. Cities often ensure adequate infrastructure for walking in new developments by requiring private developers to provide amenities such as sidewalks, bus stops, recreational trails, parks, and sites for schools.
Future work, buffeted by a strong research agenda (4), will likely enhance the specificity of these recommendations, including better specification of the population behavior and health impact, the applicability across the spectrum of demographic factors (e.g., age groups), and the expected change resulting from environmental change.
This manuscript was prepared in part through support from NIH ES014240 (BES).
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