Research articleThe Effect of Light Rail Transit on Body Mass Index and Physical Activity
Introduction
Physical inactivity in the U.S. has serious implications for obesity and its attendant comorbidities.1, 2, 3, 4, 5 Obesity can result from an excess of caloric intake versus energy exerted through routine physical activity, so even small reductions in physical activity can put individuals at risk. Post–World War II zoning laws that encouraged separating commercial, residential, and recreational land uses have promoted automobile usage over walking, biking, and public transit.6 Research has linked the associated effects of zoning laws on urban sprawl, unitary land uses, and less walkable street networks to a lack of physical activity in the population.7, 8
The health benefits of moderate and vigorous physical activity are clear.9, 10, 11, 12, 13 Less-vigorous forms of physical activity are more likely to be sustained over time, making it easier to meet exercise goals through the promotion of walking as a basic change in one's daily routine.14, 15, 16 Increasing the availability of public transit systems is one among a number of modifications to the built environment that offers some promise in increasing opportunities for physical activity and reducing the prevalence of obesity.17, 18, 19, 20 The use of public transit is associated with an increased likelihood that individuals will meet physical activity recommendations through walking.21, 22, 23, 24 Cities in the U.S. are investing in alternate forms of public transit, including the design and expansion of light rail transit systems.25 A number of studies indicate that people who walk to and from public transit obtain significantly more daily physical activity than those who do not. Minorities and lower-income individuals, groups at the greatest risk for obesity, are also more likely to receive the health benefits of walking to transit.26
Assessing the relationships between measures of the built environment and physical activity and obesity is important in order to better inform public policies regarding the effect that adaptations in the built environment can have on promoting more physically active lifestyles.27, 28, 29, 30, 31, 32, 33, 34, 35 Selection bias, however, presents a problem with cross-sectional studies investigating the link between the built environment and health outcomes.36, 37 Individuals with less economic resources may take public transit out of necessity, but they may maintain otherwise unhealthy lifestyles. On the other hand, individuals more predisposed to being physically active may choose to live in urban environments more suitably designed for healthy lifestyles.38
The current study had two primary aims. The first aim was to examine the cross-sectional associations among objective and perceived measures of the built environment, physical activity, and obesity. And the second aim was to rely on a natural experiment of the built environment induced by the introduction of a new light rail transit (LRT) line to assess the impact of transit use on obesity and physical activity levels. The use of a natural experiment and propensity score matching were intended to reduce the effects of selection bias endemic in cross-sectional studies of the effects of the built environment on health outcomes. It is hypothesized that individuals who use the LRT system will experience a significant increase over time in meeting recommended daily physical activity levels and reductions in BMI compared to similarly situated individuals who do not use LRT.
Section snippets
Methods
Data for a pre–post longitudinal study were collected on a sample of individual household members living in Charlotte NC near the site of the current South Corridor Light Rail (LRT) line. Subjects were selected through phone sampling based on census tract addresses that were within a 1-mile radius of the LRT line before it started operating. The catchment area was selected because it was within a reasonable distance from the LRT line and because the area reflected the most heavily traveled area
Results
Table 2 presents summary statistics for all baseline (T1) variables. Respondents were on average aged 52 years; a slight majority were college educated (51%); 51% were employed full-time (12% part-time, 25% unemployed, 9% disabled, and 1.5% students); and 71.3% white and 21.2% black. In terms of objective measures of the physical environment, roughly 35% of study participants had a at least one recreational park located within a half-mile radius of their household and an average of 53 food and
Discussion
The results from the initial cross-sectional analysis indicate significant associations among perceptions of neighborhood environments, BMI, obesity, and meeting weekly RPA levels. To address the issue of selection bias endemic in cross-sectional studies of the relationships among the built environment, physical activity, and obesity, a pre–post assessment was used of individuals residing in neighborhoods that were exposed to LRT. A propensity score model was used to control for baseline
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