When people drive more, they use active travel modes—such as walking and biking—less. Many research studies have suggested that providing access to public transit reduces vehicle use and encourages active transportation. However, a paper authored by recent Ph.D. graduate Alireza Ermagun and David Levinson raises the question of whether the health impacts of transit use are overstated.
“Although there appears to be evidence that transit can increase physical activity, the question becomes whether this increased physical activity actually leads to improved health measures,” says Levinson, adjunct faculty in the Department of Civil, Environmental, and Geo- Engineering (CEGE). “While some research seems to show that transit use has beneficial health impacts because it requires more walking, other studies conclude that transit might actually substitute for cycling and walking trips, leading to reduced health benefits. Additionally, transit may be self-selected by people who are already healthier or already have a more physically active lifestyle.”
To help shed light on the questions of whether and to what extent public transit use and transit accessibility affect health, Ermagun, now a post-doctoral researcher at Northwestern University, and Levinson examined the effect of transit mode share and accessibility on general health, body mass index, and height while controlling for socioeconomic, demographic, and physical activity factors. The study was built on three major data sources: share of public transit use, accessibility to jobs by transit, and obesity and health condition characteristics in 46 of the 50 largest U.S. metropolitan areas.
“We found that the transit mode share and transit accessibility did not have any significant effect on public health,” Levinson says. “We found a correlation between transit and height. Of course, we do not believe this relationship is causal—we have simply used this as an example to show the need for caution when selecting data and variables, particularly in studies with large sample sizes where ‘statistical significance’ is easily achieved.”
“What becomes clear from our study,” Ermagun adds, “is that basing the results only on ‘statistical significance’ is worthless, unless the effect of the large sample is carefully quantified as a post-analysis.”
Levinson’s ultimate hope? That the study “will help transportation policymakers and practitioners gain a clearer view of the limited health benefits of transit use and allow them to direct scarce resources in more effective directions.”
The research is discussed in a paper titled “Transit Makes You Short: On Health Impact Assessment of Transportation and the Built Environment” in the Journal of Transport and Health.
