Public transportation systems provide numerous economic benefits for a community. An added public health bonus provided by such systems may be lower obesity rates.

A new study by researchers from the University of Illinois at Urbana-Champaign and Georgia Tech compared and analyzed county data from 2001 and 2009. They found that a single percentage-point increase in mass transit ridership is associated with a 0.473 percentage-point lower obesity rate in counties across the United States.

"Opting for mass transit over driving creates opportunities for exercise that may otherwise not exist," said?Sheldon H. Jacobson, a co-author of the study and a Founder Professor of Computer Science at Illinois. "Instead of just stepping out of the house and into his car, riders need to walk from their home to a bus stop and from their stop to their destination."

The results of the study, published in the journal Transportation Research Part A: Policy and Practice, details a computational analysis of publicly available health, transportation, and census data across 227 counties from 45 states in 2001 and 2009. Differences in economic and lifestyle factors including leisure-time exercise, household income, health care coverage, and public transit funding were included in the analysis.

The new analysis is consistent with previous work by the researchers -- which found that each percentage-point increase in a county's public transit ridership was associated with a 0.221 percentage-point lower obesity rate.

"The new work takes a longitudinal approach, meaning that we examined differences between 2001 and 2009, allowing us to better control for factors that could otherwise influence the analysis," said co-author Douglas M. King, a Senior Lecturer in the Department of Industrial and Enterprise Systems Engineering at Illinois. "For example, factors like weather or physical geography that can influence the obesity rate of a county in both 2001 and 2009 are controlled since their impact is present in both time periods."

While the calculated estimates from the two studies differ in magnitude, they do not differ in a statistically significant way, the researchers note. However, both studies suggest that increasing public transit usage is associated with a reduction in a county's obesity rate.

"Because this analysis is at the county level,, the implications for an average person are not clear," Jacobson said. "The results indicate that when more people opt to use public transit, the county-level obesity rate tends to drop, though it does not necessarily imply that any one particular person is less likely to be obese if they ride transit frequently."

This study focuses on data collected in 2001 and 2009, when rail and bus were the primary modes of public transportation in the U.S.

"It will be interesting to see how Uber and Lyft, as well as bike-share programs will influence this type of analysis in the future," Jacobson said. "Our research suggests that investing in public transit can provide more efficient transportation options that not only help the environment but may also offer public health benefits."