Samuel Younkin Researches How Biking and Walking Benefits Human Health and the Planet
Bikers along Lakeshore Path in Madison, WI. Photo Credit: Bryce Richter, UW-Madison Photo Library
Active Travel Can Improve Human Health and Mitigate Climate Change
Article Author: Michael Kamp, MS
Nelson Institute for Environmental Studies
Overview
Dr. Samuel Younkin, Research Scientist at SAGE in the Nelson Institute for Environmental Studies, was not always interested in researching transportation and health. In fact, Younkin describes himself as a “jack-of-all-trades.” Younkin majored in mechanical engineering as an undergraduate, then studied math, and then completed a PhD in genetic epidemiology at Case Western Reserve University. During his PhD, Younkin studied statistical methods for genome wide association studies.
Now as a member of the Climate Solutions for Health Lab, Younkin is leveraging his combined skills in math, engineering, and epidemiology to study public health in the built urban environment. “My research is focused on estimating the impacts of transportation behavior on public health. This includes the health effects of transportation-related air pollution, road injuries, and physical activity. Our focus has been mostly on the health benefits of active travel, i.e., biking and walking, that arise due to increased physical activity,” Younkin said.
How did Younkin find himself in this avenue of research? After a postdoctoral position at John’s Hopkins, Younkin moved to Madison, Wisconsin, where he met Dr. Jason Vargo – then a member of Jonathan Patz’ lab (now the Climate Solutions for Health Lab).
Vargo was studying active travel’s benefits to human health and the research subject grabbed Younkin’s interest. Younkin joined the team to run the Integrated Transportation and Health Impacts Model (ITHIM). The model was developed by Dr. James Woodcock at Cambridge University and estimates the health benefits of active travel across three components: physical activity, air pollution, and road injuries.
Pedestrians walking down State Street and State Street Mall in Madison, Wisconsin. Photo Credit: Althea Dotzour, UW-Madison Photo Library
Younkin saw the enormous public health gains that could be made by working in active travel and felt ready to pivot from genetics research. “Our research has shown that large public health gains can be achieved through increased physical activity and, while less flashy than full genome analyses, will be more impactful on a large scale,” Younkin said.
Younkin researches how active travel improves health in two ways – improving physical health through exercise and improving environmental health by emitting less air pollution as well as less greenhouse gases. These dual benefits are termed health co-benefits because the human health benefits might not have been originally considered in climate change mitigation policy formation.
The importance of exercise is underscored by a lack of activity in the modern world, spurred by technology, the rise of working remotely, and transportation systems designed for cars. “Some researchers describe this phenomenon as an ‘epidemic of physical inactivity,’ and it’s not just a western problem, it’s global,” Younkin said. Inactivity can lead to multiple health problems. For example, the likelihood of certain diseases, such as type 2 diabetes and coronary heart disease, increase with sedentary lifestyles (1).
On the other side of the equation, driving cars and using fossil fuels also contributes to air pollution and climate change. Thus, biking and walking help improve air quality and lower the greenhouse gas emissions driving climate change.
The HOT Initiative
To address the juncture of public health and climate change, Younkin and Patz started the Health-Oriented Transportation (HOT) Initiative in 2018. The HOT Initiative was first hosted in the Global Health Institute, but now sits in the Climate Solutions for Health Lab. The HOT Initiative provides evidence of the benefits of active travel. “We think it’s important to develop evidence in terms of quantifiable results to influence policy and describe the magnitude of the problem,” Younkin said.
The HOT model provides those quantifiable results by estimating the public health co-benefits, that is human health benefits plus climate change mitigation, from increasing active travel. The model was coded in the R programming language, so it is open source. “In theory, anyone can download the HOT package, read the tutorial, every function in the HOT package is documented... and just run it like an R package,” Younkin said.
Dr. Younkin advocates for using R to conduct reproducible research. Exposure to the Bioconductor Project, gained during his research at John’s Hopkins, and UW-Madison Professor Karl Broman strongly influenced Younkin’s dedication to reproducible research. “That’s why I try to do all my work as an R package, so that it can be shared and improved,” Younkin said.
The HOT model was instrumental in a recently published paper (2) investigating how different socioeconomic characteristics affect active travel across the United States. Younkin summarized, “After controlling for variables known to influence active travel such as cars per household and population density, other socioeconomic variables also showed significant effects, such as education, income, and to a lesser extent, race and sex. Adjusting for these factors, we see that members of low-income, low-education, Black or African American, and Asian populations in US metropolitan areas are less likely to walk or cycle than high-income, high-education, or White populations, and the discrepancy in physical activity may contribute to differences in health outcomes observed across these variables.”
Currently, the HOT team is creating a web application to assess the health benefits of increasing the cycling mode share, or the proportion of trips taken by bike. For reference, the United States has a low cycling mode share, 1% according to a national survey in 2022 (3), but Madison, Wisconsin, fairs a little higher with 4% of trips taken by bike when looking solely at commuting (4).
Biking in Amsterdam
The city of Amsterdam has a high amount of trips taken per bike compared to U.S. cities.
Younkin described the functionality of the application, “If we were to increase that cycling mode share in Madison from the current value to say that of Amsterdam [35%] (5), what would the downstream health effects be?” HOT team member Henry Fremont is developing the app interface in R Shiny while Younkin is working on the underlying statistical methods.
The HOT Initiative also investigates features of cities that promote biking and walking versus driving. Looking at this phenomenon, the HOT Initiative recently finished a five-year project with the Complex Urban Systems for Sustainability and Health (CUSSH) project. The goal of CUSSH is to understand the complex systems that determine the health of cities. As part of this project, Younkin co-authored a paper (6) on the benefits of clear and rapid assessments for policymakers – very complicated models are not necessary. Younkin said, “What cities need are rapid assessments. We need to develop simple methods that are portable, communicable, and valid.”
A Healthy Future
Younkin has now spent the last eight years studying the intersection of transportation and health, and demand for his research is steadily growing. With a vision for improved public and environmental health, Younkin reemphasizes that, “Population-wide health gains could be made by creating an environment for people to be physically active without having to schedule time at a gym.” By conducting rigorous research on the health co-benefits of active travel, Dr. Samuel Younkin hopes to support a future where policy makers encourage cities to enable active, healthy lifestyles – in other words, cities designed for people instead of motorized private cars.
References
1. Lee, I. M., Shiroma, E. J., Lobelo, F., Puska, P., Blair, S. N., & Katzmarzyk, P. T. (2012). Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. The lancet, 380(9838), 219-229.
2. Younkin, S., Fremont, H., Bratburd, J., De Los Santos, D., & Patz, J. (2023). The influence of socioeconomic characteristics on active travel in US metropolitan areas and the contribution to health inequity. Wellcome Open Research, 8(266), 266.
3. National: Rates Of Biking & Walking. (2022). Benchmarking Report By the League of American Bicyclists. Retrieved September 26, 2024, from https://data.bikeleague.org/data/national-rates-of-biking-and-walking/
4. Biking & Walking Physical Activity: Madison, W: Active People, Healthy Nation. (2020). The League of American Bicyclists. Retrieved September 26, 2024 from https://data.bikeleague.org/wp-content/uploads/2022/06/LAB_APHN-Fact-Sheets_Madison_WI.pdf
5. Nello-Deakin, S., & Nikolaeva, A. (2021). The human infrastructure of a cycling city: Amsterdam through the eyes of international newcomers. Urban Geography, 42(3), 289-311.
6. Symonds, P., Milner, J., Mohajeri, N., Aplin, J., Hale, J., Lloyd, S. J., ... & Davies, M. (2020). A tool for assessing the climate change mitigation and health impacts of environmental policies: the Cities Rapid Assessment Framework for Transformation (CRAFT). Wellcome Open Research, 5.