In the United States cities have evolved rapidly toward the pattern known as sprawl, with geographically dispersed metropolitan areas, segregated land uses, heavy reliance on automobiles as the dominant transportation mode, low connectivity, and high neighborhood fragmentation. A majority of children in the United States now grow up in the suburbs. This built environment pattern has major health implications in four areas: air quality, physical activity patterns, injuries related to motor vehicle use, and “sense of community” (Frumkin, 2003). However, in all four cases, knowledge is incomplete, both in terms of understanding and assessing current problems and in terms of designing solutions. Researchers have identified key questions, and active investigations are under way. For instance, using multilevel exposure ascertainment, investigators are able to jointly assess neighborhood-level characteristics, such as collective efficacy and variations in violence, and individual-level characteristics (Sampson, Raudenbush, and Earls, 1997).
To measure physical features of a neighborhood (e.g., the exposure), many parameters of sprawl have been identified (e.g., percentage of the population living in urbanized areas, residential density, accessibility of the street network, proximity of different land uses to each other, pedestrian oriented design) (Frumkin, 2003) and combined into indices. Often these measures are limited by the availability of data; for example, in the relatively complex index proposed by Galster et al. (2000), data were available for only 13 cities. Moreover, when data are available, they can sometimes be mapped only to relatively large geographic units, such as metropolitan areas or counties. Data on smaller units, such as the census tract (geographic areas encompassing 4,000 to 6,000 individuals, with boundaries drawn to approximate neighborhood areas) or even the block, provide more information on individual and family exposures but are more elusive.
In studies of children’s health, the preferred measures of “exposure” to sprawl are perhaps best defined by what health outcomes are of interest and what biological mechanisms are hypothesized. For example, in studying the association between sprawl and physical activity, one could measure the proportion of roadway miles with sidewalks, the acreage of parkland per capita in a defined area, the mileage of bike paths, the mean distance of homes to the nearest parks, or the mean trip distance from homes to elementary schools. Such data are available from a variety of sources, including U.S. census data, Department of Transportation road data, marketing databases, and metropolitan planning agency databases.
In addition, direct observation using standardized instruments—analogous to the questionnaires used in epidemiological research—may be applied to the built environment. Such instruments need to be validated prior to use. An example of such a measurement approach is the Built Environment Site Survey Checklist (Weich et al., 2001). Using this instrument, research staff make and