Is promoting public transit an effective intervention for obesity?: A longitudinal study of the relation between public transit usage and obesity

Abstract

There is increasing evidence on the association between public transit usage and obesity. To further understand the causal impact of changes in county public transit usage on county obesity rates, this paper presents a longitudinal study on this topic. Annual health data from the Behavioral Risk Factor Surveillance System (BRFSS) and transportation data from the National Household Travel Survey (NHTS) were aggregated and matched at the county level, to create a panel data set with 227 counties from 45 states across two time periods, 2001 and 2009. Annual public transit funding, obtained from the National Transit Database (NTD), is chosen as an instrumental variable to simulate changes in public transit usage caused by exogenous changes in public policies. Possible confounding variables such as amount of leisure time physical activity, health care coverage and distribution of income are explicitly controlled. All time-invariant county level heterogeneities are implicitly controlled using first difference estimators. This study shows that promoting public transit in a county can effectively decrease the county obesity rate. Specifically, a one percentage point increase of frequent public transit riders in a county population is estimated to decrease the county population obesity rate by 0.473% points. This result supports findings in previous research that the extra amount of physical activity involved in public transit usage can have a statistically significant impact on obesity. In addition, this study also provides empirical evidence for the effectiveness of encouraging public transit usage as a public health intervention for obesity.