TRB SPECIAL REPORT 282
Does the Built Environment Influence Physical Activity?
EXAMINING THE EVIDENCE
Transportation Research Board
Transportation Research Board Special Report 282
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Copyright 2005 by the National Academy of Sciences. All rights reserved.
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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance.
This report has been reviewed by a group other than the authors according to the procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.
This study was sponsored by the Robert Wood Johnson Foundation and the Centers for Disease Control and Prevention.
Cover design by Tony Olivis, Circle Graphics.
Library of Congress Cataloging-in-Publication Data
Does the built environment influence physical activity? : examining the evidence / Committee on Physical Activity, Health, Transportation, and Land Use, Transportation Research Board, Institute of Medicine of the National Academies.
p. cm.—(Special report ; 282)
1. Urban health. 2. Transportation—Health aspects. 3. Health behavior. 4. Physical fitness. 5. Exercise. I. National Research Council (U.S.). Committee on Physical Activity, Health, Transportation, and Land Use. II. National Research Council (U.S.). Transportation Research Board. III. Institute of Medicine (U.S.). IV. Special report (National Research Council (U.S.). Transportation Research Board) ; 282.
THE NATIONAL ACADEMIES
Advisers to the Nation on Science, Engineering, and Medicine
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine.
The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chair and vice chair, respectively, of the National Research Council.
The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board’s mission is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, the Board facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provides expert advice on transportation policy and programs; and disseminates research results broadly and encourages their implementation. The Board’s varied activities annually engage more than 5,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org
Committee on Physical Activity, Health, Transportation, and Land Use
Clark University, Worcester, Massachusetts,
Bobbie A. Berkowitz,
University of Washington, Seattle,
Barbara E. Ainsworth,
San Diego State University, San Diego, California
Steven N. Blair,
Cooper Institute, Dallas, Texas
Robert B. Cervero,
University of California, Berkeley
Donald D. T. Chen,
Smart Growth America, Washington, D.C.
University of California, Los Angeles
Mindy Thompson Fullilove,
Columbia University, New York
University of Southern California, Los Angeles
T. Keith Lawton,
Metro, Portland, Oregon (retired)
Patricia L. Mokhtarian,
University of California, Davis
Kenneth E. Powell,
Georgia Department of Human Resources, Atlanta
Jane C. Stutts,
University of North Carolina, Chapel Hill
Richard P. Voith,
Econsult Corporation, Philadelphia, Pennsylvania
National Research Council Staff
Nancy P. Humphrey, Study Director,
Transportation Research Board
Carrie I. Szlyk, Program Officer,
Institute of Medicine
Public health officials have long been concerned about the effect of the environment on human health. In the nineteenth century, public health efforts in the United States were focused on controlling the spread of infectious disease, and advances in sanitation and the provision of clean water contributed to improvements in the health of the population. At the turn of the century, urban reformers adopted zoning laws and building codes to reduce the spread of disease from overcrowded conditions in central cities by lowering housing densities, as well as to separate residences from noxious commercial and industrial enterprises. Today, public health efforts are focused on the prevention of chronic disease, and the question has arisen of whether the decentralized and largely automobile-dependent development patterns that emerged in part in response to earlier public health concerns are contributing to the increasingly sedentary lifestyles of the U.S. population—a known risk factor for many chronic illnesses.
In this context, the Robert Wood Johnson Foundation and the Centers for Disease Control and Prevention requested the present study to examine the connection between the built environment and the physical activity levels of the U.S. population. In response to this request, the Transportation Research Board (TRB) and the Institute of Medicine (IOM) formed a committee consisting of 14 experts from the transportation and public health communities. The panel was chaired by Susan Hanson, Landry University Professor and Director of the Graduate School of Geography at Clark University and a member of the National Academy of Sciences. Bobbie Berkowitz, Professor and Chair of the Department of
Psychosocial and Community Health at the University of Washington’s School of Nursing and an IOM member, served as vice chair. The expertise of the panel members lies in such diverse fields as transportation demand and travel behavior, land use planning and regulation, public health, physical activity and education, economics and public policy, safety, and social and behavioral science research and methods.
To carry out its charge, the committee commissioned several papers to explore various aspects of the relationships among land use, transportation, and physical activity. The first set of three papers was written by Ross C. Brownson and Tegan Boehmer, School of Public Health, St. Louis University; Susan L. Handy, Department of Environmental Science and Policy, University of California at Davis; and Marlon G. Boarnet, Department of Planning, Policy, and Design, University of California at Irvine. These papers, respectively, examine long-term trends in land use patterns, travel behavior, employment and occupation, and time use that are related to physical activity levels; critically review the literature on these relationships, in particular for evidence of causal connections; and elaborate on the methodological and data challenges facing researchers in this area. The second set of three papers was authored by Susan D. Kirby, Kirby Marketing Solutions, Inc., and Marla Hollander, Leadership for Active Living program, San Diego State University; Anastasia Loukaitou-Sideris, School of Public Policy and Research, University of California at Los Angeles; and Michael D. Meyer and Eric Dumbaugh, School of Civil and Environmental Engineering, Georgia Institute of Technology. These papers examine the role of intervening variables that may influence individual preferences for physical activity, as well as available opportunities and choices. They address, respectively, the role of social marketing in shaping individual preferences and behavior; the importance of safety and security, both perceived and actual; and institutional and regulatory forces that affect what is built and where. The final paper, by Elliott D. Sclar, Urban Planning Program, Columbia University, and Mary E. Northridge and Emily Karpel, Mailman School of Public Health, also Columbia Univer-
sity, examines educational programs that link the fields of public health and urban planning for the purpose of training future researchers and professionals, with a focus on the need for interdisciplinary curricula and training.
All seven papers underwent extensive review and comment by the committee and were revised numerous times. They are listed in Appendix A, along with the addresses where they can be accessed on the Internet. The reader is cautioned that the interpretations and conclusions drawn in the papers are those of their authors; the key findings endorsed by the committee appear in the body of this report.
The committee also drew from a paper on the role of segregation and poverty in limiting choices for physical activity among disadvantaged populations, written by Benjamin P. Bowser, Department of Sociology and Social Services, California State University at Hayward. Dr. Bowser raised many important issues that stimulated discussion among the committee and at a workshop (see below) regarding the special problems of physical activity for these populations. Many of these issues are covered in this report.
Recognizing that the above papers could not fully represent the relatively new but rapidly growing field of research linking the built environment to physical activity levels, the committee held a workshop midway through the project to involve a broader audience of experts drawn from academia, consulting firms, professional associations, advocacy groups, state and federal agencies, congressional staff, and the press. At this workshop, each paper was presented and critiqued by a commentator, then discussed by the invited participants. The workshop concluded with a wrap-up by two rapporteurs—one from the physical activity and one from the transportation community. Of the more than 160 individuals invited to the workshop, 46 attended in addition to the committee, commentators, rapporteurs, and staff. Their names and affiliations, along with the workshop agenda, can be found in Appendix B. The commentary and critiques offered during the workshop were considered in both finalizing the authored papers and preparing this final report.
The committee also supplemented its expertise by receiving briefings at its meetings from a wide range of experts. In particular, the committee thanks Robert T. Best, President of Westar Associates, and Thomas Lee, former CEO of the Newhall Land and Farming Company—two California developers who discussed their experience with building large planned communities amenable to walking and cycling. The committee also thanks Donald H. Pickrell, Chief Economist at the U.S. Department of Transportation’s John A. Volpe National Transportation Systems Center, for his presentation on requirements for establishing the connections among urban form, travel, and physical activity; Karla Henderson, Professor and Chair, Department of Recreation and Leisure Studies, University of North Carolina at Chapel Hill, who spoke on the role of recreational facilities in increasing physical activity; Roland Sturm, Senior Economist, the RAND Corporation, for his presentation on the economics of physical inactivity; and Leslie S. Linton, Deputy Director of Active Living Research, a program funded by the Robert Wood Johnson Foundation and housed at San Diego State University, for her update on program-sponsored research related to this study.
This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s (NRC’s) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that assist the authors and NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The content of the review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. The committee thanks the following individuals for their participation in the review of this report: Hank Dittmar, Reconnecting America, Las Vegas, New Mexico; Robert Dunphy, Urban Land Institute, Washington, D.C.; Jonathan Fielding, Department of Health Services, Los Angeles County, California; William Fischel, Dartmouth College, Hanover, New Hampshire; Lester Hoel, University of Vir-
ginia, Charlottesville; Russell Pate, University of South Carolina, Columbia; Joseph Schofer, Northwestern University, Evanston, Illinois; Boyd Swinburn, Deakin University, Melbourne, Australia; and Martin Wachs, University of California, Berkeley.
Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the committee’s conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Enriqueta C. Bond, Burroughs Wellcome Fund, and C. Michael Walton, University of Texas at Austin. Appointed by NRC, they were responsible for making certain that an independent examination of the report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
Nancy P. Humphrey of TRB, together with Carrie I. Szlyk of IOM, managed the study. Both drafted sections of the final report under the guidance of the committee and the supervision of Stephen R. Godwin, Director of Studies and Information Services at TRB, and Rose Martinez, Director of the Board on Health Promotion and Disease Prevention at IOM. Suzanne Schneider, Associate Executive Director of TRB, managed the report review process. Special appreciation is expressed to Rona Briere, who edited the report. Amelia Mathis assisted with meeting arrangements and communications with committee members, Jocelyn Sands handled contracting with the paper authors, and Alisa Decatur provided word processing support for preparation of the final manuscript. In the TRB Publications Office, Jennifer Weeks prepared the final manuscript and the commissioned papers for posting on the web; Norman Solomon provided final editorial guidance; and Juanita Green managed the book design and production, under the supervision of Javy Awan.
Accelerometer. A monitoring device that measures the intensity of an activity.
Accessibility. Distance to or from destinations or facilities.
Body mass index (BMI). One of the most commonly used measures for defining overweight and obesity, calculated as weight in pounds divided by the square of height in inches, multiplied by 703.
Built environment. Defined broadly to include land use patterns, the transportation system, and design features that together provide opportunities for travel and physical activity. Land use patterns refer to the spatial distribution of human activities. The transportation system refers to the physical infrastructure and services that provide the spatial links or connectivity among activities. Design refers to the aesthetic, physical, and functional qualities of the built environment, such as the design of buildings and streetscapes, and relates to both land use patterns and the transportation system.
Case-control studies. Studies in which exposure to an acknowledged risk factor is compared between individuals from the same population with and without a condition. For example, individuals could be sorted on the basis of their activity level (e.g., active versus sedentary) into case and control groups to see whether there are statistically significant differences in environmental characteristics that may influence the propensity of the two groups to be physically active.
Connectivity. The directness of travel to destinations.
Context-sensitive design. A project development process encompassing geometric design that attempts to address safety and efficiency while being responsive to or consistent with a road’s natural and human environment.
Cross-sectional studies. Studies that examine the relationship between conditions (e.g., physical activity behaviors) and other variables of interest in a defined population at a single point in time. Cross-sectional studies can quantify the presence and magnitude of associations between variables. Unlike longitudinal studies, however, they cannot be used to determine the temporal relationship between variables, and evidence of cause and effect cannot be assumed.
Cul-de-sac. A street, lane, or passage closed at one end.
Decentralization. Movement of population and employment away from city centers.
Deconcentration. Movement of population and employment to less-dense areas.
Demand theory. Derived from economics and psychology, posits that individuals make decisions in their self-interest, given the option to do so. In other words, most choices are made on the basis of their feasibility and their relative costs and benefits to the individual. Thus, for example, one would assume that people would be more likely to walk if walking trips became more pleasant, safer, or in any sense easier, or if alternatives to walking became more costly or more difficult.
Density. Typically measured as employment or population per square mile.
Ecological models. Based on social cognitive theory, which explains behavior in terms of reciprocal relationships among the characteristics of
a person, the person’s behavior, and the environment in which the behavior is performed. Ecological models emphasize the role of the physical as well as the social environment.
Edge cities. A term coined by Washington Post journalist and author Joel Garreau in 1991 that refers to suburban cities, typically located near major freeway intersections.
Energy expenditure. Represents the sum of three factors: (a) resting energy expenditure to maintain basic body functions (approximately 60 percent of total energy requirements); (b) processing of food, which includes the thermic effect of digestion, absorption, transport, and deposition of nutrients (about 10 percent of total requirements); and (c) nonresting energy expenditure, primarily in the form of physical activity (about 30 percent of total requirements).
Energy imbalance. The situation that occurs when energy intake (calories consumed) exceeds or is less than total daily energy expenditure. Weight gain occurs when energy intake exceeds total daily energy expenditure for a prolonged period.
Exercise. A subcategory of physical activity defined as that which is planned, structured, repetitive, and purposive in the sense that improvement or maintenance of one or more components of physical fitness is the objective.
Experimental studies. Studies in which subjects are randomly assigned to the exposures of interest and followed for the outcome of interest. The most persuasive scientific evidence of causality usually is derived from experimental studies of individuals. The important advantages of experimental studies are that researchers have considerable control over all aspects of the study, including the type of exposure, the selection of subjects, and the assignment of exposure to the subjects.
Geographic information system (GIS). An automated system for the capture, storage, retrieval, analysis, and display of spatial data.
Global Positioning System (GPS). A worldwide radionavigation system comprising a constellation of 24 satellites and their ground stations. GPS uses these “man-made stars” as reference points to calculate positions accurate to a matter of meters.
Health. A state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity.
Land use mix. Diversity or variety of land uses (e.g., residential, commercial, industrial).
Longitudinal studies. Studies in which individuals are known to have various levels of exposure and are followed over time to determine the incidence of outcomes. Quasi-experimental designs and natural experiments are two categories of longitudinal studies. Quasi-experimental designs are those in which the exposure is assigned but not according to a randomized experimental protocol. Investigators lack full control over the dose, timing, or allocation of subjects, but conduct the study as if it were an experiment. Natural experiments are situations in which different groups in a population have differing exposures and can be observed for different outcomes. Neither type of design is really an experiment because researchers have not randomly assigned the individuals to exposure groups.
Metabolic equivalent (MET). A unit used to estimate the metabolic cost (oxygen consumption) of physical activity. Activities that raise the rate of energy expenditure are frequently expressed as the ratio of working to resting metabolic rate.
Metropolitan statistical area (MSA). A statistical geographic entity consisting of at least one core urbanized area with a population of 50,000 or more. The MSA comprises the central county or counties containing the core and adjacent outlying counties with a high degree of social and economic integration with the central county, as measured through commuting ties with the counties containing the core.
Neotraditional developments. Developments whose design is characterized by land use and street patterns that encourage walking and cy-
cling. These include such features as interconnected street networks, sidewalks, walking and cycling paths, mixed land uses, and higher densities than those of more typical suburban developments. Also known as new-urbanist developments.
Nonmotorized travel. Travel by nonmotorized means, including walking, cycling, small-wheeled transport (e.g., skates, skateboards, push scooters, hand carts), and wheelchair.
Obesity and overweight. Adults are defined as being obese if they have a body mass index (BMI) of 30 or greater, and as being overweight if they have a BMI of 25 but less than 30. Children and adolescents are defined as overweight if they have a BMI above the 95th percentile for their age and sex. A definition of obesity for children and adolescents on the basis of health outcomes or risk factors has not yet been formulated.
Overlay district. A planning tool that provides for special zoning requirements that are tailored to the characteristics of a particular area (e.g., special architectural character) or complementary to a particular public policy (e.g., higher-density building near rail transit stations) and are an exception to the underlying zoning.
Pedometer. A monitoring device that counts steps and measures distance.
Physical activity. Bodily movement produced by the contraction of skeletal muscle that increases energy expenditure above the basal (i.e., resting) level.
Physical fitness. The ability to carry out daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and to respond to unforeseen emergencies. Attributes of physical fitness include such characteristics as cardiorespiratory endurance; flexibility; balance; body composition; and muscular endurance, strength, and power.
Self-selection bias. In lay terms, refers to the need to distinguish the roles of personal attitudes, preferences, and motivations from external influences on observed behavior. For example, do people walk more in
a particular neighborhood because of pleasant tree-lined sidewalks, or do they live in a neighborhood with pleasant tree-lined sidewalks because they like to walk? If researchers do not properly address this issue by identifying and separating these effects, their empirical results will be biased in the sense that features of the built environment may appear to influence physical activity more than they in fact do. (See Chapter 5 for a more technical definition of self-selection bias.)
Social marketing. The application of commercial marketing techniques to the analysis, planning, execution, and evaluation of programs designed to influence the voluntary behavior of target audiences, with the aim of improving their personal welfare and that of their society.
Traffic calming. Measures that attempt to slow traffic speeds in residential neighborhoods and near schools and pedestrian ways through physical devices designed to be self-enforcing. These include vertical deflections (speed humps and bumps and raised intersections); horizontal deflections (serpentines, bends, and deviations in a road); road narrowing (via neck-downs and chokers); and medians, central islands, and traffic circles.
Transit-oriented developments. Projects that involve mixed-use development (i.e., residential and commercial) near public transit stations.